Rather use a proper alpha channel if we need transparency.
This is another small step towards merged alpha in our vcl
layer.
I suspect the intent in a lot of this code was to save memory.
Which have been a thing way back then, but these days our
backends mostly end up doing a copy-and-convert to a real
alpha channel anyway, so the existing code is actually
now a pessimisation.
Change-Id: I4a2bcbb2f76b841f05bc00580f364492829c69de
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/114808
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
b153d147c9