[ts][threejs] Blending mode not working properly

[davidetan]

It appears that blending modes are not working properly.

This behaviour can be easily reproduced by loading celestial-circus an observing the eyes of the character.

[davidetan]

Blending formula for Multiply is different in Threejs.

This problem is addressed by the changes from this branch: https://github.com/EsotericSoftware/spine-runtimes/tree/three-pma