Don't insert resource links for @mentions that have been removed from the message editor (#35831)

Release Notes:

- N/A

crates/editor/src/editor.rs

@@ -2705,6 +2705,11 @@ impl Editor {
         self.completion_provider = provider;
     }
 
+    #[cfg(any(test, feature = "test-support"))]
+    pub fn completion_provider(&self) -> Option<Rc<dyn CompletionProvider>> {
+        self.completion_provider.clone()
+    }
+
     pub fn semantics_provider(&self) -> Option<Rc<dyn SemanticsProvider>> {
         self.semantics_provider.clone()
     }