desc
introduce rust-analyzer into meta repo. it can be either new USE_FLAG in dev-lang/rust and dev-lang/rust-bin or a separate package

disclaimer
subject of this ticket is related to rust LSP - it means that only users that develop in rust on Funtoo machine will benefit from it.

rust compiler and other building related stuff is out of scope here

background
1. RLS (current/former rust LSP) is beeing deprecated: https://blog.rust-lang.org/2022/07/01/RLS-deprecation.html

Builds of RLS will continue to be released until at least the Rust 1.64 release (2022-09-22), after which no new releases will be made. This timeline may change if any issues arise.

(...)

After the end of release builds of RLS, we plan to replace the rls executable in official Rust releases with a small LSP implementation that informs the user that RLS is no longer available.

2. it already is replaced by rust-analyzer
3. we have a USE flag rls in both dev-lang/rust and dev-lang/rust-bin