Add handling for INS, DEL, NUM LOCK, and some shifted characters.

[freakboy3742]

Adds some missing key definitions for INSERT, DELETE and NUMLOCK, and some other esoteric keys; and improves shift handling for GTK.

Fixes #2220.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[rmartin16]

These work; although, do you want to handle CTRL, ALT, and SUPER similarly to shift? I still see those warnings.

Also, when I tab to the Calculate button in Tutotial1 example, I get a system beep. Is that expected?

[freakboy3742]

These work; although, do you want to handle CTRL, ALT, and SUPER similarly to shift? I still see those warnings.

I've just added handling for these.

Also, when I tab to the Calculate button in Tutotial1 example, I get a system beep. Is that expected?

... it is not. Bother. It was being masked in my testing because my VM didn't have its "speaker" attached.

[freakboy3742]

The beep appears to be pre-existing... I've opened #2554 to track it.

[rmartin16]

One more interesting one...if I hold CTRL or ALT and then press SUPER, I can still get the warning for SUPER...not necessarily a common combo but it is used by window placement mgmt.

Also, just as note, noticing that the ALT+TAB icon is using the system default on Ubuntu and Fedora....may just be a Gnome thing though.

[freakboy3742]

The CTRL+ALT+WIN key combo appears to be coming through as a completely different key, rather than a combination of the three individual keys - but you can bind to MOD_1+MOD_2+MOD_3+a.

Based on the GTK docs, all this handling is a bit abstract anyway, because it can be redefined at the X11 level - I'm guessing that is what is happening here.

Rather than try to chase our tail here, I've opted to add a generic "If unknown, be quiet" handler; this only impacts on the key handling in TextInput, so I think we're OK to ignore weird combos.

[rmartin16]

This tradeoff makes sense. fwiw, looks like Android also just ignores undefined keys.