completion_metrics.dart change, don't expect completions when the completed token would be a dynamic type.

This change improves the number of successful completions from 96.2% to 98.2% on the collection library.

Change-Id: I6dffa3b6ad6c92be482ca0810c1c0aa558fdcbde
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/133545
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Jaime Wren <jwren@google.com>

pkg/analysis_server/tool/completion_metrics/visitors.dart

@@ -652,6 +652,11 @@ class ExpectedCompletionsVisitor extends RecursiveAstVisitor {
         node.thisOrAncestorOfType<ArgumentList>() != null) {
       return false;
     }
+
+    // If the type of the SimpleIdentifier is dynamic, don't include.
+    if (node.staticType != null && node.staticType.isDynamic) {
+      return false;
+    }
     return true;
   }
 }