Fix key type map entry with unbound vmod not ignored
Currently we only ignore key type map entries with non-zero mods and
with a zero modifier mask. However, the XKB protocol states ([source]):
> Map entries which specify unbound virtual modifiers are not considered.
So we currently handle `map[Unbound]` key type map entries (all modifiers
unbound) but not `map[Bound+Unbound]` entries (mix of bound and unbound
modifiers).
Fixed by properly checking unbound modifiers on each key type map entry.
This also fixes a test that was accidentally passing.
[source]: https://www.x.org/releases/X11R7.7/doc/kbproto/xkbproto.html#:~:text=Map%20entries%20which%20specify%20unbound%20virtual%20modifiers,not%20considered
tests: Modifier and group latch
- Added a big bunch of tests for modifier latch. No yet exhaustive,
but should cover the most usual use cases.
- Added missing test cases for breaking the group latch. Ideally, more
tests should be added to match the coverage of modifiers latches.
WARNING: it is ambiguous what prevents a latch when multiple keys are
*simultenously* operated together. We currently assuming that
any action that is not identical to the considered latch
prevents it.
