Improve handling of expressions in patterns

Closes rust-lang#112593.

Methodcalls' dots in patterns are silently recovered as commas (e.g. `Foo("".len())` -> `Foo("", len())`) so extra diagnostics are emitted:
```rs
struct Foo(u8, String, u8);

fn bar(foo: Foo) -> bool {
    match foo {
        Foo(4, "yippee".yeet(), 7) => true,
        _ => false
    }
}
```
```
error: expected one of `)`, `,`, `...`, `..=`, `..`, or `|`, found `.`
 --> main.rs:5:24
  |
5 |         Foo(4, "yippee".yeet(), 7) => true,
  |                        ^
  |                        |
  |                        expected one of `)`, `,`, `...`, `..=`, `..`, or `|`
  |                        help: missing `,`

error[E0531]: cannot find tuple struct or tuple variant `yeet` in this scope
 --> main.rs:5:25
  |
5 |         Foo(4, "yippee".yeet(), 7) => true,
  |                         ^^^^ not found in this scope

error[E0023]: this pattern has 4 fields, but the corresponding tuple struct has 3 fields
 --> main.rs:5:13
  |
1 | struct Foo(u8, String, u8);
  |            --  ------  -- tuple struct has 3 fields
...
5 |         Foo(4, "yippee".yeet(), 7) => true,
  |             ^  ^^^^^^^^ ^^^^^^  ^ expected 3 fields, found 4

error: aborting due to 3 previous errors
```

This PR checks for patterns that ends with a dot and a lowercase ident (as structs/variants should be uppercase):
```
error: expected a pattern, found a method call
 --> main.rs:5:16
  |
5 |         Foo(4, "yippee".yeet(), 7) => true,
  |                ^^^^^^^^^^^^^^^ method calls are not allowed in patterns

error: aborting due to 1 previous error
```

Also check for expressions:
```rs
fn is_idempotent(x: f32) -> bool {
    match x {
        x * x => true,
        _ => false,
    }
}

fn main() {
    let mut t: [i32; 5];
    let t[0] = 1;
}
```
```
error: expected a pattern, found an expression
 --> main.rs:3:9
  |
3 |         x * x => true,
  |         ^^^^^ arbitrary expressions are not allowed in patterns

error: expected a pattern, found an expression
  --> main.rs:10:9
   |
10 |     let t[0] = 1;
   |         ^^^^ arbitrary expressions are not allowed in patterns
```

Would be cool if the compiler could suggest adding a guard for `match`es, but I've no idea how to do it.

---
`@rustbot` label +A-diagnostics +A-parser +A-patterns +C-enhancement

Rollup of 9 pull requests

Successful merges:

 - rust-lang#116677 (References refer to allocated objects)
 - rust-lang#118625 (Improve handling of expressions in patterns)
 - rust-lang#120266 (Improve documentation for [A]Rc::into_inner)
 - rust-lang#120373 (Adjust Behaviour of `read_dir` and `ReadDir` in Windows Implementation: Check Whether Path to Search In Exists)
 - rust-lang#120390 (Borrow check inline const patterns)
 - rust-lang#120420 (Stop using derivative in rustc_pattern_analysis)
 - rust-lang#120428 (hir: Two preparatory changes for rust-lang#120206)
 - rust-lang#120453 (Fix incorrect comment in normalize_newlines)
 - rust-lang#120462 (Clean dead code)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup of 9 pull requests

Successful merges:

 - rust-lang#116677 (References refer to allocated objects)
 - rust-lang#118625 (Improve handling of expressions in patterns)
 - rust-lang#120266 (Improve documentation for [A]Rc::into_inner)
 - rust-lang#120373 (Adjust Behaviour of `read_dir` and `ReadDir` in Windows Implementation: Check Whether Path to Search In Exists)
 - rust-lang#120390 (Borrow check inline const patterns)
 - rust-lang#120420 (Stop using derivative in rustc_pattern_analysis)
 - rust-lang#120428 (hir: Two preparatory changes for rust-lang#120206)
 - rust-lang#120453 (Fix incorrect comment in normalize_newlines)
 - rust-lang#120462 (Clean dead code)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#118625 - ShE3py:expr-in-pats, r=WaffleLapkin

Improve handling of expressions in patterns

Closes rust-lang#112593.

Methodcalls' dots in patterns are silently recovered as commas (e.g. `Foo("".len())` -> `Foo("", len())`) so extra diagnostics are emitted:
```rs
struct Foo(u8, String, u8);

fn bar(foo: Foo) -> bool {
    match foo {
        Foo(4, "yippee".yeet(), 7) => true,
        _ => false
    }
}
```
```
error: expected one of `)`, `,`, `...`, `..=`, `..`, or `|`, found `.`
 --> main.rs:5:24
  |
5 |         Foo(4, "yippee".yeet(), 7) => true,
  |                        ^
  |                        |
  |                        expected one of `)`, `,`, `...`, `..=`, `..`, or `|`
  |                        help: missing `,`

error[E0531]: cannot find tuple struct or tuple variant `yeet` in this scope
 --> main.rs:5:25
  |
5 |         Foo(4, "yippee".yeet(), 7) => true,
  |                         ^^^^ not found in this scope

error[E0023]: this pattern has 4 fields, but the corresponding tuple struct has 3 fields
 --> main.rs:5:13
  |
1 | struct Foo(u8, String, u8);
  |            --  ------  -- tuple struct has 3 fields
...
5 |         Foo(4, "yippee".yeet(), 7) => true,
  |             ^  ^^^^^^^^ ^^^^^^  ^ expected 3 fields, found 4

error: aborting due to 3 previous errors
```

This PR checks for patterns that ends with a dot and a lowercase ident (as structs/variants should be uppercase):
```
error: expected a pattern, found a method call
 --> main.rs:5:16
  |
5 |         Foo(4, "yippee".yeet(), 7) => true,
  |                ^^^^^^^^^^^^^^^ method calls are not allowed in patterns

error: aborting due to 1 previous error
```

Also check for expressions:
```rs
fn is_idempotent(x: f32) -> bool {
    match x {
        x * x => true,
        _ => false,
    }
}

fn main() {
    let mut t: [i32; 5];
    let t[0] = 1;
}
```
```
error: expected a pattern, found an expression
 --> main.rs:3:9
  |
3 |         x * x => true,
  |         ^^^^^ arbitrary expressions are not allowed in patterns

error: expected a pattern, found an expression
  --> main.rs:10:9
   |
10 |     let t[0] = 1;
   |         ^^^^ arbitrary expressions are not allowed in patterns
```

Would be cool if the compiler could suggest adding a guard for `match`es, but I've no idea how to do it.

---
`@rustbot` label +A-diagnostics +A-parser +A-patterns +C-enhancement

Add `PatKind::Err` to AST/HIR

#116715 added `thir::PatKind::Error`; this PR adds `hir::PatKind::Err` and `ast::PatKind::Err` (see rust-lang/rust#118625 (comment).)

---

``@rustbot`` label +A-patterns
r? WaffleLapkin

Add `PatKind::Err` to AST/HIR

#116715 added `thir::PatKind::Error`; this PR adds `hir::PatKind::Err` and `ast::PatKind::Err` (see rust-lang/rust#118625 (comment).)

---

``@rustbot`` label +A-patterns
r? WaffleLapkin

Further improve diagnostics for expressions in pattern position

Follow-up of rust-lang#118625, see rust-lang#121697.

```rs
fn main() {
    match 'b' {
        y.0.0.1.z().f()? as u32 => {},
    }
}
```
Before:
```
error: expected one of `=>`, ``@`,` `if`, or `|`, found `.`
 --> src/main.rs:3:10
  |
3 |         y.0.0.1.z().f()? as u32 => {},
  |          ^ expected one of `=>`, ``@`,` `if`, or `|`
```
After:
```
error: expected a pattern, found an expression
 --> src/main.rs:3:9
  |
3 |         y.0.0.1.z().f()? as u32 => {},
  |         ^^^^^^^^^^^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
  |
help: consider moving the expression to a match arm guard
  |
3 |         val if val == y.0.0.1.z().f()? as u32 => {},
  |         ~~~ +++++++++++++++++++++++++++++++++
help: consider extracting the expression into a `const`
  |
2 +     const VAL: /* Type */ = y.0.0.1.z().f()? as u32;
3 ~     match 'b' {
4 ~         VAL => {},
  |
help: consider wrapping the expression in an inline `const` (requires `#![feature(inline_const_pat)]`)
  |
3 |         const { y.0.0.1.z().f()? as u32 } => {},
  |         +++++++                         +
```

---

r? fmease
`@rustbot` label +A-diagnostics +A-parser +A-patterns +C-enhancement