Fix and clean up utterly confused (and confusing) transition tests

Various QDateTime tests relating to transitions
* used a nomenclature that made them confusing to thing about; and
* expected identically-initiallized variables to behave differently.

The latter, naturally, lead to "expected fail" tests.

Rewrote the tests to get the date-times they want to test at by means
that avoid the ambiguities inherent in QDateTime's lack of a way to
distinguish the two passes through the repeated hour in a fall-back
(QTBUG-79923) and added commented-out tests indicating what should be
true once that ambiguity is resolved. Verified the DST status is as
expected in the cases where that's the correct distinction between
date-times with the same date and time. Renamed various things to
(hopefully) make them more intelligible.

In the process, purged some leading 0s from numbers in code.

Fixes: QTBUG-68936
Change-Id: Id7a348995238b70dcb81a96edb8a3fa5315f86fa
Reviewed-by: Thiago Macieira <[email protected]>