library: fix some stability annotations
This PR updates some stability attributes to correctly reflect when some items actually got stabilized. Found while testing https://github.com/rust-lang/rust/pull/132481.
### `core::char` / `std::char`
In https://github.com/rust-lang/rust/pull/26192, the `core::char` module got "stabilized" for 1.2.0, but the `core` crate itself was still unstable until 1.6.0.
In https://github.com/rust-lang/rust/pull/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 https://github.com/rust-lang/rust/pull/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 https://github.com/rust-lang/rust/pull/95956 to existing yet.
Then, `core::array` got stabilized and `std::array` got added, first targeting 1.36.0 in https://github.com/rust-lang/rust/pull/60657, but then getting backported for 1.35.0 in https://github.com/rust-lang/rust/pull/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.
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