Add Abgr32 pixel type

[antonfirsov]

Follow up on #1344 (comment)

We have: Rgba32, Argb32, Bgra32
Abgr32 looks like a missing piece. Can be optimized using existing patterns.

[ynse01]

Now that #1886 is merged into master, we can close this issue, right?

[JimBobSquarePants]

Yep! Thanks!