Extract lua language support into an extension (#10437)

Release Notes:

- Extracted lua language support into an extension, and improved Lua
highlighting and completion label styling.

---------

Co-authored-by: Marshall <marshall@zed.dev>

extensions/lua/languages/lua/embedding.scm

@@ -0,0 +1,10 @@
+(
+    (comment)* @context
+    .
+    (function_declaration
+        "function" @name
+        name: (_) @name
+        (comment)* @collapse
+        body: (block) @collapse
+    ) @item
+)