Don't prompt on renaming markdown files

Add two extra checks:
- Don't prompt users if the file extension doesn't change
- Don't prompt if only optional editors are available

src/vs/workbench/contrib/customEditor/browser/customEditors.ts

@@ -325,10 +325,15 @@ export class CustomEditorService extends Disposable implements ICustomEditorServ
 		this._webviewHasOwnEditFunctions.set(possibleEditors.length > 0);
 	}
 
-	private async handleMovedFileInOpenedFileEditors(_oldResource: URI, newResource: URI): Promise<void> {
+	private async handleMovedFileInOpenedFileEditors(oldResource: URI, newResource: URI): Promise<void> {
+		if (extname(oldResource) === extname(newResource)) {
+			return;
+		}
+
 		// See if the new resource can be opened in a custom editor
-		const possibleEditors = this.getAllCustomEditors(newResource).allEditors;
-		if (!possibleEditors.length) {
+		if (!this.getAllCustomEditors(newResource).allEditors
+			.some(editor => editor.priority !== CustomEditorPriority.option)
+		) {
 			return;
 		}