canvas_item shader_type

[novalis]

Feature/enhancement description:

For 2d textures in Godot, the shader_type is canvas_item, and output goes to COLOR= in the vertex() function (rather than fragment()). There should be a new type of material, called something like "Dynamic 2D material" to support this.

[novalis]

material_2d.txt

Something like this -- but I have no idea what to do for Unity or Unreal, so ignore those parts.

[RodZill4]

I guess this could just be an export option of the dynamic unlit material.