MetaWindowActor: Sync thawed state when surface actor is set

Not having a surface actor would cause the window actor state to be
considered frozen, thus causing various state (such as geometry, shape
etc) synchronization to be delayed until thawed. If the window actor
was "thawed" due to having a surface set, not all state would be
properly synchronized, causing the thawed window actor to be displayed
incorrectly.

This patch fixes this by putting state synchronization after thawing in
a common function, calling it both from frozen count decreasing and
surface setting.

This fixes for example misplaced menus in Steam.

https://bugzilla.gnome.org/show_bug.cgi?id=770991