The `MovementAtExclusiveEnd` test was improperly authored for the
following reasons:
- it should have used `TEST_METHOD_PROPERTY` to cover all of the
TextUnits
- TextUnit::Document (arguably one of the most important) was ommitted
accidentally (`!= TextUnit_Document` was used instead of `<=`)
- The created range was not `EndExclusive`, but rather, the last cell in
the buffer (`EndInclusive`)
The first half of this PR fixes the test.
The second half of this PR expands the test and fixes any related issues
to make the test pass (i.e. #7771):
- `TEST_METHOD_PROPERTY` was added for it to be degenerate (start/end at
`EndExclusive`) or not (last cell of buffer)
- `utr->_start` is now also validated after moving backwards
NOTE: `utr->_start` was not validated when moving forwards because
moving forwards should always fail when at/past the last chell in the
buffer.
Closes#7771
e401edf9ef