Contrary to what you can read on the internet, SGCAPS keys don't work
by having capslock toggle the KBDCTRL bit, they actually have two
consecutive table entries, the first of which is for the normal
version and the second of which is for the capslocked version.
Background: SGCAPS is short for Swiss German caps because Swiss German
was the first layout to use this feature. For keys with the SGCAPS flag,
capslock has a different effect than pressing shift. For example:
Shift + ü = è, CapsLock + ü = Ü, CapsLock + Shift + ü = È
DLL loading failures should not happen under normal circumstances, but
we should at least try not to crash and and print better diagnostic
messages if they do happen.
See https://gitlab.gnome.org/GNOME/gtk/-/issues/4610
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
The old code used repeated calls to `ToUnicodeEx` to populate
the translation table, which is slow and buggy. The new code
directly loads the layout driver DLLs from Windows.
See https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/4338
