Fix Emits of Additional ANSI Characters

[schrieveslaach]

This commit ensures that ANSI chars won't be emitted when pressing non-standard modifier keys.

Fixes #4975

[op3]

This does not catch all possible keys that should be silent. For example, using the neo layout, I can press Shift + ISO_Level3_Shift + Tab, which results in ISO_Level5_Lock. The current nightly version and also this patch still emit a Tab key, even though no key should be emitted.

(there are also a few typos in the comment in the code)

[schrieveslaach]

@op3, thanks for testing. Do you see more missing keys? If not, I would update my PR with the aforementioned missing keys.

[op3]

So, ISO_Level3_Lock and ISO_Level5_Lock would be missing, obviously.

Another key combination that should not result in any characters is ISO Level5 Shift + 4. This key combination is not assigned and thus is not supposed to do anything, but the current code tries to find a fallback (which would be 4).

Obviously, this is much less of a problem than the modifier keys, because one would usually not press this key combination. Still, I would consider this to be incorrect behavior. And adding “4” to the list of exceptions also does not feel right (too specific …).

There are a few more unassigned key combinations. The W, A, and Z keys on layer 5 come to mind.

[schrieveslaach]

@wez, does this fix provide a solution that you would consider to be merged?