Use rust-analyzer from path if possible (#12418)

Release Notes:

- Added support for looking up the `rust-analyzer` binary in `$PATH`. This allows using such tools as `asdf` and nix to configure per-folder rust installations. To enable this behavior, use the `path_lookup` key when configuring the `rust-analyzer` `binary`: `{"lsp": {"rust-analyzer": {"binary": {"path_lookup": true }}}}`.

crates/project/src/project_settings.rs

@@ -94,6 +94,7 @@ const fn true_value() -> bool {
 pub struct BinarySettings {
     pub path: Option<String>,
     pub arguments: Option<Vec<String>>,
+    pub path_lookup: Option<bool>,
 }
 
 #[derive(Clone, Debug, Default, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]