Fixing keyboard bugs in a portable way

[David Richmond]

On a separate thread, Richard and I were discussing problems with the keyboard shortcuts on MacOS.

I did a little digging, and it seems that this issue of hardware keycodes is not even platform-independent on Linux: https://www.berrange.com/tags/key-codes/

So, I replaced the direct keycode logic in dnm_clean_event () with a GDK call that pulls out what GDK calls the "first level" for a given hardware code. We can just pass the hardware code from the key event to get it. That gives us back, for example, lowercase letters instead of uppercase with shift, and numbers on the top-row number keys instead of, e.g., the parentheses.

I opened a pull request on github with the relevant changes. I would love to hear testing feedback on multiple platforms. As I mentioned, I am a very inexperienced developer, so hopefully I didn't break anything else with this change. I am also worried that I did not implement g_free() correctly at core/kbd-custom.c:169-170. Am I actually freeing the returned array? The double pointer syntax in the GDK docs is very confusing. The documentation for the GDK call I'm using is here: https://developer.gnome.org/gdk3/stable/gdk3-Keyboard-Handling.html#gdk-keymap-get-entries-for-keycode.

This change immediately fixes all apparent keyboard shortcut issues for me on the Mac.

David