Restore color sync feature

[Cub0use]

Detailed description of your suggestion

I miss the color syncing feature a lot since it was removed in 4.9 (even without the opacity syncing https://github.com/JannisX11/blockbench/issues/1693).

It was very useful to have 2 Blockbench windows opened: one to texture a model, and another one to color pick from another model.

Reference images are great, but observing a model and color picking on the fly was superior when texturing a model based on another one.

Alternatively, the Reference Model plugin could be interesting to update to suit that need and keep everything in a single Blockbench window. Allowing to open json models and placing them like reference images, with a little gizmo to make them rotate, zoom in and out etc.