Add Support for Spine's Premultiplied Alpha Mode

[johanzhu]

To improve the rendering of Spine animations, especially when dealing with transparent textures, we need to add support for premultiplied alpha mode. This will allow for more accurate blending and improve the visual quality of animations.

Goals:

• Implement premultiplied alpha mode support in the Spine runtime.
• Ensure that this mode can be easily toggled on or off depending on the project's requirements.
• Update the rendering pipeline to handle premultiplied textures correctly.
• Maintain compatibility with existing features and workflows.