[3.50] Support mix feature in global animation and private animation both

[rexrainbow]

In 3.50-beta4, mix is set in animation manager if 2 global animations are existed. It can't support mix for private animation created by sprite.anims.create(). It is nice that mix feature also can support global animation and private animation both.
A possible solution might be, put responding mix in each animation object, to store transition delay of previous animation.

[photonstorm]

Yeah I did consider this. I was thinking about making mix based on a frame name/number, instead of delay, too.