Fixes https://github.com/flutter/flutter/issues/74114

This PR addresses the issue detailed here: https://github.com/flutter/flutter/issues/74114 . The boolean isExpanded returned by the expansion panel callback now reflects the state of the panel that the user is seeing. If it's expanded on screen then the callback returns true. When you close the panel the callback returns false. When another panel is open and you open a different one, the callback executes twice. It returns isExpanded == false for the panel you are closing and true for the panel that is being opened.
I had to change the code in a couple existing tests because some tests are using the old behavior of the callback. This PR addresses feedback listed in closed PR -> https://github.com/flutter/flutter/pull/127876 . The reasone the original PR is closed is that I was having some struggles with git. A couple of the commits in this PR are just reverts of commits I meant not to happen.
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