Obtains a list of keycode/group/level combinations that will generate
Groups and levels are two kinds of keyboard mode; in general, the level determines whether the top or bottom symbol on a key is used, and the group determines whether the left or right symbol is used.
On US keyboards, the shift key changes the keyboard level, and there are no groups. A group switch key might convert a keyboard between Hebrew to English modes, for example.
`GdkEventKey` contains a group field that indicates the active keyboard group. The level is computed from the modifier mask.
The returned array should be freed with g_free.
a keyval, such as gdk_key_a, gdk_key_up, gdk_key_return, etc.
return location for an array of `GdkKeymapKey`
return location for number of elements in returned array
true if keys were found and returned