Previously, the accessibility semantics for Checkboxes on Windows platform applications did not update when the state (checked/unchecked) of the widget changed. It seems to me that this was the result of an overly-restrictive check that only propagated updates to this status for Radio widgets, excluding Checkboxes. That is fixed in this PR and a unit test is added to ensure that state changes to Checkboxes are properly reflected.

Addresses issue flutter/flutter#96218 in the Flutter repo.

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 and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See testing the engine for instructions on
  writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

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