build: Use libxkbcommon to resolve keysyms

[ueno]

Although it's still a bit ugly, this implements what I outlined in:
#47 (review)

[ueno]

@lo48576 would you like to review this?

[lo48576]

Thanks, I'll try this patch soon (tomorrow if possible).

[ueno]

Thank you!

[lo48576]

With this patch (and fcitx-skk), Control key is wrongrly handled.
(Shift key seems to behave as same, so I think there is an issue around modifier key handling.)

1. Ctrl key confirms preedit
   input: A o SPC Control_L (not at skk command, in real world)
   expected: ▼青 (not confirmed)
   got: 青 (confirmed)

2. Ctrl key removes incomplete alphabet at hiragana mode
   input: H o h Control_L (in real world)
   expected: ▽ほh (not confirmed)
   got: ▽ほ (not confirmed)

3. After Ctrl key, normal input is ignored?
   input: H o h Control_L a a a a a (in real world)
   expected: ▽ほはああああ
   got: ▽ほ
   At this state, Backspace key correctly removes character ほ.

[ueno]

Thank you for the report and I am sorry for the long delay. Indeed, it seems that unassigned keysyms were treated as commit in some cases; it should be fixed in 10555a2.

[lo48576]

Tested "Muhenkan" and "Escape" bindings on my environment, and they worked as I expected. 😄

[ueno]

Thank you for testing; let's merge it then.