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/clangd_ext.rs

@@ -9,7 +9,7 @@ use crate::lsp_ext::find_specific_language_server_in_selection;
 
 use crate::{element::register_action, Editor, SwitchSourceHeader};
 
-static CLANGD_SERVER_NAME: &str = "clangd";
+const CLANGD_SERVER_NAME: &str = "clangd";
 
 fn is_c_language(language: &Language) -> bool {
     return language.name() == "C++".into() || language.name() == "C".into();

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()