landing "Convert internal vcl bitmap formats transparency->alpha (II)"

[Noel Grandin <noelgrandin@xxxxxxxxx>]

Hi

So want to finally land this change:

    https://gerrit.libreoffice.org/c/core/+/114168

Which is a very important step towards getting combined-alpha (i.e. 32-bit bitmaps) working in LibreOffice.

However, there is one small glitch - there is a unit test which I have had to disable on macos, because neither myself Patrick Luby have been able to reproduce the failure locally on our macs, but it fails quite reliably on jenkins.

I expect that at some point someone will log a regression bug which will lead more directly to the problem and then I can fix it.

Any objections?

Regards, Noel Grandin