drop OutputDevice::GetBitmapEx in favour of returning Bitmap

as part of the project of removing BitmapEx in favour of Bitmap, now that we can store RGBA data in Bitmap.

This mostly just moves the Bitmap->BitmapEx from inside OutputDevice to the various call sites,
from where I can make further improvements.

Change-Id: Id5366c1eb5ebca98fee7c974737552f4a09a5c2f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/188341
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

cppcanvas/source/mtfrenderer/transparencygroupaction.cxx

@@ -383,9 +383,9 @@ namespace cppcanvas::internal
                     // update buffered bitmap and transformation
                     BitmapSharedPtr aBmp( VCLFactory::createBitmap(
                                               mpCanvas,
-                                              aVDev->GetBitmapEx(
+                                              BitmapEx(aVDev->GetBitmap(
                                                   aBitmapPoint,
-                                                  aBitmapSizePixel ) ) );
+                                                  aBitmapSizePixel ) ) ));
                     mxBufferBitmap = aBmp->getUNOBitmap();
                     maLastTransformation = aTotalTransform;
                     maLastSubset = rSubset;