Don't set isFinal for synthetic properties in ElementBuilder, set isStatic.
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 <1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com>
Reviewed-by: Samuel Rawlins <5cf2cac5eec2ad6d0eb2b0f4ff6af9a590ce2bf6@google.com>
Commit-Queue: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk