Implement TextServer GDExtension interface, remove TextServer GDNative interface.

modules/text_server_fb/config.py

@@ -9,3 +9,13 @@ def configure(env):
 def is_enabled():
     # The module is disabled by default. Use module_text_server_fb_enabled=yes to enable it.
     return False
+
+
+def get_doc_classes():
+    return [
+        "TextServerFallback",
+    ]
+
+
+def get_doc_path():
+    return "doc_classes"