Initial implementation of Vector Displacement Channel

[ucupumar]

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
• [ ] 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