Don't set isFinal for synthetic properties in ElementBuilder, set isStatic.

Similar to https://dart-review.googlesource.com/c/sdk/+/201780

Change-Id: Ie82aae2ae88a6947ef57a73aae76a99a2bae85e1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/202162
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: scheglov

pkg/analyzer/lib/src/summary2/element_builder.dart

@@ -956,7 +956,6 @@ class ElementBuilder extends ThrowingAstVisitor<void> {
       if (property == null) {
         var variable = TopLevelVariableElementImpl(name, -1);
         variable.isSynthetic = true;
-        variable.isFinal = accessorElement.isGetter;
         _enclosingContext.addTopLevelVariable(name, variable);
         property = variable;
       }
@@ -967,7 +966,7 @@ class ElementBuilder extends ThrowingAstVisitor<void> {
       if (property == null) {
         var field = FieldElementImpl(name, -1);
         field.isSynthetic = true;
-        field.isFinal = accessorElement.isGetter;
+        field.isStatic = accessorElement.isStatic;
         _enclosingContext.addField(name, field);
         property = field;
       }