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/settings/src/settings_store.rs

@@ -114,6 +114,7 @@ pub trait Settings: 'static + Send + Sync {
 pub struct SettingsJsonSchemaParams<'a> {
     pub staff_mode: bool,
     pub language_names: &'a [String],
+    pub font_names: &'a [String],
 }
 
 /// A set of strongly-typed setting values defined via multiple JSON files.