This is a reattempt to fix #87194.

The previous attempt #87240 was reverted because many internal tests was written in a way that sets the view configuration at the beginning of a file and expect to use it throughout the file, which was broken by the previous method.

void main() {
  binding.renderView.configuration = TestViewConfiguration(size: const Size(900, 900));
  testWidget('test1', ...);
  testWidget('test2', ...);
}

This PR restores the surface size and the view configuration in the following strategy:

• The surface size is always reset to null at postTest, since the surface size can not be changed out of tests.
• The view configuration is recorded at reset (the pre-test hook), and is restored to that value at postTest.

I tested this change against some previously failing tests and they have been passing.

This PR also removes the temporary teardown cleanup in viewport_test.dart.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt.
• All existing and new tests are passing.

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