Initial implementation of Vector Displacement Channel

Since Eevee next can do displacement in realtime, vector displacement channel is more possible to implement

[x] Add vector displacement type to normal channel and create a node output for that
[x] Sculpt vector displacement image using multires
[x] Dealing with layer and channel intensity when going into sculpt mode
[x] For safety, Make user cannot edit any layer when entering sculpt mode
[x] Add new VDM layer on new layer option
[x] Enable subdiv setup when first creating new VDM layer
[x] Baking vector displacement map
[x] Dealing with user that already use multires
[x] Dealing with layer channel override
[x] Check older blender compatibility (Sculpt image only available for Blender 3.2+)

Later targets

Dealing with transfer UV
Currently Geometry nodes does not support UDIM so create a workaround about that
Dealing with mirror modifier
Sculpting a non YZ flipped image
Use vdm as normal when write height or subdiv setup are off (can also be useful for smooth vdm normal)
Advance subdiv setup setting when creating new vdm layer for the first time
Add vdm layer from a shape key

ucupumar / ucupaint