Fix another TODO in elements printer, use 'name'.

Change-Id: I6696a4b559072b064ee16d22b8aad528b52eb6a0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/312704
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: scheglov

pkg/analyzer/test/src/summary/element_text.dart

@@ -622,8 +622,18 @@ class _ElementWriter {
   }
 
   void _writeName(Element e) {
-    // TODO(scheglov) Use 'name' everywhere.
-    var name = e is ConstructorElement ? e.name : e.displayName;
+    final String name;
+    switch (e) {
+      case ExtensionElement(name: null):
+        name = '<null>';
+      default:
+        name = e.name!;
+    }
+
+    if (e is PropertyAccessorElement && e.isSetter) {
+      expect(name, endsWith('='));
+    }
+
     _sink.write(name);
     _sink.write(name.isNotEmpty ? ' @' : '@');
     _sink.write(e.nameOffset);