Only make the use-dot-operator-to-call-method suggestion, but do not
double down and use the recovered type to perform method call
typechecking as it will produce confusing diagnostics on the "fixed"
code.

fix comment on Allocator trait

fixes rust-lang#107040

…cked, r=WaffleLapkin

Uplift `clippy::invalid_utf8_in_unchecked` lint

This PR aims at uplifting the `clippy::invalid_utf8_in_unchecked` lint into two lints.

## `invalid_from_utf8_unchecked`

(deny-by-default)

The `invalid_from_utf8_unchecked` lint checks for calls to `std::str::from_utf8_unchecked` and `std::str::from_utf8_unchecked_mut` with an invalid UTF-8 literal.

### Example

```rust
unsafe {
    std::str::from_utf8_unchecked(b"cl\x82ippy");
}
```

### Explanation

Creating such a `str` would result in undefined behavior as per documentation for `std::str::from_utf8_unchecked` and `std::str::from_utf8_unchecked_mut`.

## `invalid_from_utf8`

(warn-by-default)

The `invalid_from_utf8` lint checks for calls to `std::str::from_utf8` and `std::str::from_utf8_mut` with an invalid UTF-8 literal.

### Example

```rust
std::str::from_utf8(b"ru\x82st");
```

### Explanation

Trying to create such a `str` would always return an error as per documentation for `std::str::from_utf8` and `std::str::from_utf8_mut`.

-----

Mostly followed the instructions for uplifting a clippy lint described here: rust-lang#99696 (review)

```@rustbot``` label: +I-lang-nominated
r? compiler

-----

For Clippy:

changelog: Moves: Uplifted `clippy::invalid_utf8_in_unchecked` into rustc

…lor-9, r=notriddle

Migrate GUI colors test to original CSS color format

Follow-up of rust-lang#111459.

The `browser-ui-test` update is a fix when converting the alpha value to hex format. More information [here](GuillaumeGomez/browser-UI-test#511).

r? ```@notriddle```

Don't typecheck recovered method call from suggestion

Only make the use-dot-operator-to-call-method suggestion, but do not double down and use the recovered type to perform method call typechecking as it will produce confusing diagnostics relevant for the *fixed* code.

### Code Sample

```rust
struct Client;

impl Client {
    fn post<T: std::ops::Add>(&self, _: T, _: T) {}
}

fn f() {
    let c = Client;
    post(c, ());
}
```

### Before This PR

```
error[[E0277]](https://doc.rust-lang.org/stable/error_codes/E0277.html): cannot add `()` to `()`
 --> src/lib.rs:9:5
  |
9 |     post(c, ());
  |     ^^^^^^^^^^^ no implementation for `() + ()`
  |
  = help: the trait `Add` is not implemented for `()`
note: required by a bound in `Client::post`
 --> src/lib.rs:4:16
  |
4 |     fn post<T: std::ops::Add>(&self, _: T, _: T) {}
  |                ^^^^^^^^^^^^^ required by this bound in `Client::post`

error[[E0061]](https://doc.rust-lang.org/stable/error_codes/E0061.html): this function takes 2 arguments but 1 argument was supplied
 --> src/lib.rs:9:5
  |
9 |     post(c, ());
  |     ^^^^ an argument of type `()` is missing
  |
note: method defined here
 --> src/lib.rs:4:8
  |
4 |     fn post<T: std::ops::Add>(&self, _: T, _: T) {}
  |        ^^^^                   -----  ----  ----
help: provide the argument
  |
9 |     post((), ())(c, ());
  |         ++++++++

error[[E0425]](https://doc.rust-lang.org/stable/error_codes/E0425.html): cannot find function `post` in this scope
 --> src/lib.rs:9:5
  |
9 |     post(c, ());
  |     ^^^^ not found in this scope
  |
help: use the `.` operator to call the method `post` on `&Client`
  |
9 -     post(c, ());
9 +     c.post(());
  |

Some errors have detailed explanations: E0061, E0277, E0425.
For more information about an error, try `rustc --explain E0061`.
```

### After This PR

```
error[E0425]: cannot find function `post` in this scope
 --> tests/ui/typeck/issue-106929.rs:9:5
  |
9 |     post(c, ());
  |     ^^^^ not found in this scope
  |
help: use the `.` operator to call the method `post` on `&Client`
  |
9 -     post(c, ());
9 +     c.post(());
  |

error: aborting due to previous error

For more information about this error, try `rustc --explain E0425`.
```

Fixes rust-lang#106929.