Merge #8767

8767: implement range formatting r=matklad a=euclio

Fixes #7580.

This PR implements the `textDocument/rangeFormatting` request using `rustfmt`'s `--file-lines` option.

Still needs some tests. What I want to know is how I should handle the instability of the `--file-lines` option. It's still unstable in rustfmt, so it's only available on nightly, and needs a special flag to enable. Is there a way for `rust-analyzer` to detect if it's using nightly rustfmt, or for users to opt-in?

Co-authored-by: Andy Russell <arussell123@gmail.com>

diff --cc crates/rust-analyzer/src/config.rs
Simple merge

diff --cc crates/rust-analyzer/src/handlers.rs
Simple merge

diff --cc crates/rust-analyzer/src/main_loop.rs
Simple merge