ngl: implement atlas compaction

ngl: implement atlas compaction

This required finishing up the begin_frame/end_frame semantics for
GskNglTextureLibraryw which was apparently overlooked.

The driver was changed to provide more information to the library when
beginning frames. We do not need to use end_frame so that was removed.

The frame age is the same as GL (60) but I do wonder if that is based
on seconds if we should be using something longer for situations where
we have higher frame rates.

Fixes #3771