gdkkeys-win32: Fix capslock handling

gdkkeys-win32: Fix capslock handling

Previously, we treated CapsLock and KanaLock as part of the global
keyboard state, much like NumLock and ScrollLock, rather than using
the supplied modifier mask. This was because GDK does not have a
modifier mask for KanaLock, only for CapsLock, so it would not have been
possible to properly support it.

However, this approach ended up causing problems, with certain keyboard
shortcuts not registering when capslock was active. This was first
observed in Inkscape [0] and appears to affect shortcuts consisting of a
single key (like 'a') with no additional modifiers (wheareas shortcuts
like 'ctrl+a' work).

So now we are using the supplied GDK_LOCK_MASK instead, and dropped
support for KanaLock, which we probably don't need anyway (since regular
text input should be handled by the IME input module -- the keymap is
mainly for shortcuts and keybindings, where you don't really want
KanaLock).

[0] https://gitlab.com/inkscape/inkscape/-/issues/3082