Bake Target Refactor

[ucupumar]

The current bake target works as an addition to the main channel bake function. This causes some inefficiency because the main channel always needs to be baked first before doing the bake target. It's better to rethink the system and make the bake target the main system for baking node channels in ucupaint.

This is the possible to-do list for the bake target refactor

• Implement vertex color bake target
• Convert the Bake to vertex color toggle on the main channel as a vertex color bake target
• Convert the original bake channel function into an image bake target, so baking node channels will always use a bake target
• Implement radio buttons to switch between different bake target outputs when Use Baked is enabled
• Move the bake target UI above the channel