Add Feature to Create Mask Sprite Object

[Aodaruma]

Is your feature request related to a problem? Please describe.
I think it should be good to add a feature for creating and managing mask sprites

Describe the solution you'd like

• mask sprite object is created using splines or polygons
• add an operator to facilitate the creation of mask sprites
• the operator generates automatically empty shape keys from target sprites at creation, and links these to the target shape key parameters via drivers
• mask sprites should be material-less and displayed as wireframes in the viewport
• masking with composite nodes to using view layers
• it should be excluded when sprites are exporting for Godot (or set holdout material?)