Revert "Remove CoreGui from PLUGIN_ONLY_CLASSES" (#1339)

Reverts #1337

API dump lies. You can't actually access this at all.

<img width="643" alt="image"
src="https://github.com/user-attachments/assets/6e3f722f-8729-4c24-8b20-ed1db57b7fe1"
/>

src/constants.ts

@@ -26,6 +26,7 @@ export const CREATABLE_BLACKLIST = new Set([
 export const PLUGIN_ONLY_CLASSES = new Set([
 	"ABTestService",
 	"ChangeHistoryService",
+	"CoreGui",
 	"DataModelSession",
 	"DebuggerBreakpoint",
 	"DebuggerManager",