shaped-texture: Reintroduce clip_region
In commit 4c1fde9d MetaCullable related code was moved out of MetaShapedTexture into MetaSurfaceActor. While generally desirable, this removed drawing optimizations in MetaShapedTexture for partial redraws. The common case for fully obscured actors was still supposed to work, but it was now discovered that it actually did not.
This commit revert parts of 4c1fde9d: it reintroduces clipping to MetaShapedTexture but leaves all culling and actor related logic in MetaSurfaceActor.
Thanks to Daniel van Vugt for uncovering the issue.
This is an alternative fix to !1324 (closed)