VCL: remove comment, rename ImplInitClipRegion to InitClipRegion

Change-Id: If8d18b59285f75d61d9972ca019390fce700be3c
VCL: Rearrange clipping functions in outdev.hxx

Change-Id: Ieb6ce1f3505d1f2d6949fe0c4da762f4aead6d83
fdo#74702 Move GetActiveClipRegion code into Window

Window checks to see if the window is currently being painted, then it
checks to see if there is an active clipping region (which it needs to
intersect with).

Printer and VirtualDevice don't have this need, so they just return the
clipping region.

Change-Id: I1a9af237940f5add725c783c02a193c9e3329fa6