Further improving TAPL error messages

Old:
java.lang.AssertionError: http://go/tapl test failure:
Context: getting widget No Config in widgets list => resulting visible state is Widgets;
Details: Widgets container didn't become scrollable

New:
java.lang.AssertionError: http://go/tapl test failure: Widgets container didn't become scrollable;
Context: getting widget No Config in widgets list; now visible state is Widgets

Test: local runs
Bug: 187761685
Change-Id: I77a5b9133f577af27182f823e1130c371863e065