fix: make rust-analyzer could auto start

[ClSlaid]

patch refers to:
simrat39/rust-tools.nvim#397 (comment)

[ayamir]

Does this issue really exist? My rust-analyzer can start automatically when I nvim main.rs.

[ClSlaid]

Does this issue really exist? My rust-analyzer can start automatically when I nvim main.rs.

If your rust-analyzer is not installed from mason, but from rustup, package managers or other sources, it will not automatically start and attach.

[Jint-lzxy]

I'm a bit dubious about whether this PR really fixes the problem. AFAIU it's possible that the FileType event is triggered after the server(s) get attached, so the (newly) registered server isn't spawned by lspconfig automatically. Maybe a better solution is to explicitly tell lspconfig to load the new schema after rust-tools completes its startup (just blindly guessing, haven't verified this yet).

[ayamir]

I'm a bit dubious about whether this PR really fixes the problem.

No, it doesn't work for me though the rust-analyzer installed from rustup and it can be found in my PATH. Close it.
The best way to avoid it is install it by mason.