The key controller was consuming key events
for modifier keys, for no entirely convincing
reason, which leads to problems when somebody
actually listens for those, such as the simple
input method does for C-S-u processing.
(cherry-picked from 91d6893f02)
Closes: https://gitlab.gnome.org/GNOME/gtk/issues/1884
This adds specific marshallers for all of the locations where a generic
marshaller is being used. It also provides va_marshallers to reduce the
chances that we get stack traces from perf going through ffi_call_unix64.
If we set c_marshaller manually, then g_signal_newv() will not setup a
va_marshaller for us. However, if we provide c_marshaller as NULL, it will
setup both the c_marshaller (to g_cclosure_marshal_VOID__VOID) and
va_marshaller (to g_cclosure_marshal_VOID__VOIDv) for us.
This event controller is meant to replace usage from key-press/release-event
handlers all through. Optionally it can be set a GtkIMContext, so interaction
is carried by the controller.
