Improve performance of JSON schema creation (#6770)

JSON LSP adapter now caches the schema. `workspace_configuration` is
back to being async, and we are also no longer asking for font names
twice while constructing the schema.
Release Notes:
- Improved performance when opening the .json files.

---------

Co-authored-by: Kirill <kirill@zed.dev>

crates/language/src/language.rs

@@ -342,7 +342,7 @@ pub trait LspAdapter: 'static + Send + Sync {
         None
     }
 
-    fn workspace_configuration(&self, _: &Path, _: &mut AppContext) -> Value {
+    fn workspace_configuration(&self, _workspace_root: &Path, _cx: &mut AppContext) -> Value {
         serde_json::json!({})
     }