Enable key events during IME composition

[slouken]

Fixes #10486

[slouken]

@Kontrabant, can you help me with this one on Linux?

[Kontrabant]

The checks that filter key presses if an IME is active are simple to remove, but the problem is that some desktops eat the key events themselves if a compose sequence is active, so the key events just never arrive in the first place. I know Gnome eats key presses, not sure about KDE or wlroots based ones.

[Kontrabant]

I checked again with testime, and X11 already passes through key events even for dead keys on both Gnome and KDE. On Wayland, with text input active:

• By default, Gnome eats keys that are part of dead-key composition sequences or IME
• By default, KDE passes dead keys as part of composition sequences for Latin character layouts (e.g. accented characters on US international with dead keys), but keys are eaten as soon as something like IBus+Anthy is in use.

In short, Linux backends already pass key events though if they get them, but it's not guaranteed that they will always get them since an IME can eat them first, and we have no control over that.

[slouken]

It turns out that some platforms just don't provide key events for IME composition (Wayland, among others) and in general you shouldn't be assuming that key events will come through for all text input. The original bug is going to be resolved a different way, so we'll go ahead and close this.