Move more completion override tests to run on both protocols.

Change-Id: I082fdd06918cc6589314f9e3e0bab68ee52e28d9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/244726
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Phil Quitslund <pquitslund@google.com>

Author: scheglov

pkg/analysis_server/lib/src/services/completion/dart/suggestion_builder.dart

@@ -974,7 +974,7 @@ class SuggestionBuilder {
         withNullability: _isNonNullableByDefault);
     _addSuggestion(
       suggestion,
-      textToMatchOverride: element.displayName,
+      textToMatchOverride: _textToMatchOverride(element),
     );
   }
 
@@ -1502,6 +1502,13 @@ class SuggestionBuilder {
       suggestion.docSummary = doc.summary;
     }
   }
+
+  static String _textToMatchOverride(ExecutableElement element) {
+    if (element.isOperator) {
+      return 'operator';
+    }
+    return element.displayName;
+  }
 }
 
 abstract class SuggestionListener {