… stabilized

I don't know how to test this. I confirmed locally that this gives the
appropriate help with `channel = "beta"`:

```
error[E0554]: `#![feature]` may not be used on the beta release channel
 --> src/lib.rs:2:1
  |
2 | #![feature(min_const_generics)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the attribute
  |
  = help: the feature `min_const_generics` has been stable since 1.51.0 and no longer requires an attribute to enable

error[E0554]: `#![feature]` may not be used on the beta release channel
 --> src/lib.rs:3:1
  |
3 | #![feature(min_const_generics, min_specialization)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: the feature `min_const_generics` has been stable since 1.51.0 and no longer requires an attribute to enable

error[E0554]: `#![feature]` may not be used on the beta release channel
 --> src/lib.rs:4:1
  |
4 | #![feature(box_patterns)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^
```

Add missing information on what standard-library features are supported
by the UEFI targets.

All current UEFI targets (which is i686 and x86_64) only support no_std
cross-compilations. `std` support has not been worked on and is unlikely
to emerge anytime soon, due to the much restricted environment that UEFI
provides.

On most From implementations, the docstring is attached to the
function. This is also how people have been [recommended] to do it.

Screenshots:

* [before](https://user-images.githubusercontent.com/1593513/115767662-323c5480-a35e-11eb-9918-98aba83e9183.png)
* [after](https://user-images.githubusercontent.com/1593513/115767675-35374500-a35e-11eb-964f-c28eeb6c807a.png)

[recommended]: rust-lang#51430 (comment)

Fixes: rust-lang#84421

This was missed a while ago when support for proc-macro attributes was
first added.

On stable, suggest removing `#![feature]` for features that have been stabilized

I don't know how to test this (https://rust-lang.zulipchat.com/#narrow/stream/182449-t-compiler.2Fhelp/topic/Run.20tests.20without.20enabling.20nightly.20features.3F). I confirmed locally that this gives the
appropriate help with `channel = "beta"`:

```
error[E0554]: `#![feature]` may not be used on the beta release channel
 --> src/lib.rs:2:1
  |
2 | #![feature(min_const_generics)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the attribute
  |
  = help: the feature `min_const_generics` has been stable since 1.51.0 and no longer requires an attribute to enable

error[E0554]: `#![feature]` may not be used on the beta release channel
 --> src/lib.rs:3:1
  |
3 | #![feature(min_const_generics, min_specialization)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: the feature `min_const_generics` has been stable since 1.51.0 and no longer requires an attribute to enable

error[E0554]: `#![feature]` may not be used on the beta release channel
 --> src/lib.rs:4:1
  |
4 | #![feature(box_patterns)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^
```

Closes rust-lang#83715.

implement `TrustedRandomAccess` for `Take` iterator adapter

`TrustedRandomAccess` requires the iterator length to fit within `usize`. `take(n)` only constrains the upper bound of an iterator. So if the inner is `TrustedRandomAccess` (which already implies a finite length) then so can be `Take`.

``````@rustbot`````` label T-libs-impl

…es, r=varkor

various const parameter defaults improvements

Actually resolve names in const parameter defaults, fixing `struct Foo<const N: usize = { usize::MAX }>`.

---
Split generic parameter ban rib for types and consts, allowing
```rust
#![feature(const_generics_defaults)]
struct Q;
struct Foo<T = Q, const Q: usize = 3>(T);
```

---
Remove the type/const ordering restriction if `const_generics_defaults` is active, even if `const_generics` is not. allowing us to stabilize and test const param defaults separately.

---
Check well formedness of const parameter defaults, eagerly emitting an error for `struct Foo<const N: usize = { 0 - 1 }>`

---
Do not forbid const parameters in param defaults, allowing `struct Foo<const N: usize, T = [u8; N]>(T)` and `struct Foo<const N: usize, const M: usize = N>`. Note that this should not change anything which is stabilized, as on stable, type parameters must be in front of const parameters, which means that type parameter defaults are only allowed if no const parameters exist.

We still forbid generic parameters inside of const param types.

r? ``````@varkor`````` ``````@petrochenkov``````

Clean up .gitignore

Categorizes entries in the `.gitignore` file.

Other changes:
- added `desktop.ini` (Windows equivalent of `.DS_Store`)
- removed `.hg/` and `.hgignore`

Move `sys_common::poison` to `sync::poison`

`sys_common` should not contain publicly exported types, only platform-independent abstractions on top of `sys`, which `sys_common::poison` is not. There is thus no reason for the module to not live under `sync`.

Part of rust-lang#84187.

…r=dtolnay

Ensure TLS destructors run before thread joins in SGX

The excellent test is from ``@jethrogb``

For context see: rust-lang#83416 (comment)

doc/platform-support: clarify UEFI support

Add missing information on what standard-library features are supported by the UEFI targets.

All current UEFI targets (which is i686 and x86_64) only support no_std cross-compilations. `std` support has not been worked on and is unlikely to emerge anytime soon, due to the much restricted environment that UEFI provides.

…=jsha

Prevent control, shift and alt keys to make search input lose focus

Part of rust-lang#84384.

r? ```@jsha```

…d-items-toggle, r=yaahc

doc: Get rid of "[+] show undocumented items" toggle on numeric From impls

On most From implementations, the docstring is attached to the function. This is also how people have been [recommended] to do it.

Screenshots:

* [before](https://user-images.githubusercontent.com/1593513/115767662-323c5480-a35e-11eb-9918-98aba83e9183.png)
* [after](https://user-images.githubusercontent.com/1593513/115767675-35374500-a35e-11eb-964f-c28eeb6c807a.png)

[recommended]: rust-lang#51430 (comment)

Fix ICE if original_span(fn_sig) returns a span not in body sourcefile

Fixes: rust-lang#84421

r? ```@tmandry```

fyi: ```@wesleywiser``` ```@sdroege``` ```@rajivshah3```

rustdoc: Get rid of `clean::TypeKind`

It does exactly the same thing as ItemType.