Use const over static for string literals (#18635)

I noticed a few places where we were storing `&'static str`s in
`static`s instead of `const`s.

This PR updates them to use `const`.

Release Notes:

- N/A

crates/editor/src/rust_analyzer_ext.rs

@@ -10,7 +10,7 @@ use crate::{
     ExpandMacroRecursively,
 };
 
-static RUST_ANALYZER_NAME: &str = "rust-analyzer";
+const RUST_ANALYZER_NAME: &str = "rust-analyzer";
 
 fn is_rust_language(language: &Language) -> bool {
     language.name() == "Rust".into()