This commit shards the all-encompassing `core`, `std_misc`, `collections`, and `alloc` features into finer-grained components that are much more easily opted into and tracked. This reflects the effort to push forward current unstable APIs to either stabilization or removal. Keeping track of unstable features on a much more fine-grained basis will enable the library subteam to quickly analyze a feature and help prioritize internally about what APIs should be stabilized.

A few assorted APIs were deprecated along the way, but otherwise this change is just changing the feature name associated with each API. Soon we will have a dashboard for keeping track of all the unstable APIs in the standard library, and I'll also start making issues for each unstable API after performing a first-pass for stabilization.

This commit shards the all-encompassing `core`, `std_misc`, `collections`, and `alloc` features into finer-grained components that are much more easily opted into and tracked. This reflects the effort to push forward current unstable APIs to either stabilization or removal. Keeping track of unstable features on a much more fine-grained basis will enable the library subteam to quickly analyze a feature and help prioritize internally about what APIs should be stabilized.

A few assorted APIs were deprecated along the way, but otherwise this change is just changing the feature name associated with each API. Soon we will have a dashboard for keeping track of all the unstable APIs in the standard library, and I'll also start making issues for each unstable API after performing a first-pass for stabilization.

…richton

This seems to have slipped through the cracks in #26192.

r? @alexcrichton

library: fix some stability annotations

This PR updates some stability attributes to correctly reflect when some items actually got stabilized. Found while testing rust-lang#132481.

### `core::char` / `std::char`

In rust-lang#26192, the `core::char` module got "stabilized" for 1.2.0, but the `core` crate itself was still unstable until 1.6.0.

In rust-lang#49698, the `std::char` module was changed to a re-export of `core::char`, making `std::char` appear as "stable since 1.2.0", even though it was already stable in 1.0.0.

By marking `core::char` as stable since 1.0.0, the docs will show correct versions for both `core::char` (since 1.6.0) and `std::char` (since 1.0.0). This is also consistent with the stabilities of similar re-exported modules like `core::mem`/`std::mem` for example.

### `{core,std}::array` and `{core,std}::array::TryFromSliceError`

In rust-lang#58302, the `core::array::TryFromSliceError` type got stabilized for 1.34.0, together with `TryFrom`. At that point the `core::array` module was still unstable and a `std::array` re-export didn't exist, but `core::array::TryFromSliceError` could still be named due to rust-lang#95956 to existing yet.

Then, `core::array` got stabilized and `std::array` got added, first targeting 1.36.0 in rust-lang#60657, but then getting backported for 1.35.0 in rust-lang#60838.

This means that `core::array` and `std::array` actually got stabilized in 1.35.0 and `core::array::TryFromSliceError` was accessible through the unstable module in 1.34.0 -- mark them as such so that the docs display the correct versions.

Rollup merge of rust-lang#132482 - lukas-code:stab-attrs, r=Noratrieb

library: fix some stability annotations

This PR updates some stability attributes to correctly reflect when some items actually got stabilized. Found while testing rust-lang#132481.

### `core::char` / `std::char`

In rust-lang#26192, the `core::char` module got "stabilized" for 1.2.0, but the `core` crate itself was still unstable until 1.6.0.

In rust-lang#49698, the `std::char` module was changed to a re-export of `core::char`, making `std::char` appear as "stable since 1.2.0", even though it was already stable in 1.0.0.

By marking `core::char` as stable since 1.0.0, the docs will show correct versions for both `core::char` (since 1.6.0) and `std::char` (since 1.0.0). This is also consistent with the stabilities of similar re-exported modules like `core::mem`/`std::mem` for example.

### `{core,std}::array` and `{core,std}::array::TryFromSliceError`

In rust-lang#58302, the `core::array::TryFromSliceError` type got stabilized for 1.34.0, together with `TryFrom`. At that point the `core::array` module was still unstable and a `std::array` re-export didn't exist, but `core::array::TryFromSliceError` could still be named due to rust-lang#95956 to existing yet.

Then, `core::array` got stabilized and `std::array` got added, first targeting 1.36.0 in rust-lang#60657, but then getting backported for 1.35.0 in rust-lang#60838.

This means that `core::array` and `std::array` actually got stabilized in 1.35.0 and `core::array::TryFromSliceError` was accessible through the unstable module in 1.34.0 -- mark them as such so that the docs display the correct versions.