gdkkeys-win32: Fix handling of SGCAPS

gdkkeys-win32: Fix handling of SGCAPS

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