``premul_alpha`` should also count global alpha

[bilhox]

Everything is in the title.

In my opinion we should either add a kwargs global_alpha to the method or make the function count the global alpha set on the surface.

[ActualCannibalPanda]

Anyone working on this, or can hop in on it?

[bilhox]

Hi @RobertGameDev , sure you can work on it !

[ActualCannibalPanda]

Apologies for the delay, should have this sorted before the week is out