Replace _XkbTypedRealloc & _XkbClearElems with new _XkbResizeArray

Makes resizing & clearing more consistent and gets rid of some weird
quirks like always subtracting 1 from the size passed to _XkbClearElems
so it could always add 1 to the size passed in.

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>