TryReserveError is not re-exported

[CeleritasCelery]

The version of TryReserveError from allocator_api2 is not publicly re-exported, so it cannot be named in types. Unless there is a specific reason for this, it seems like it should be exported to make it at least as useful as the std-lib version.

Also the docs for try_reserve still reference the one in std::collections.

[zakarumych]

Should've been fixed in a16a359038cf741aa6445809e33a845e17e58c0d

[amunra]

~It looks like the fix introduced by https://github.com/zakarumych/allocator-api2/commit/a16a359038cf741aa6445809e33a845e17e58c0d no longer appears in stable/mod.rs.~

~In other words, the bug is still there and the Vec::try_reserve API can't be compiled without nightly.~

It looks like the latest released crate version doesn't have this patch somehow, but the latest code in the main branch does.