Grease Pencil - Global and Local UV coordinates for Gradient and Texture materials

Add the ability to select Global and Local uv coordinates to Gradient and Texture materials . The local coordinates would use the bounding rect min/max extents of the stroke and the global coordinates would be, ugh, global (maybe initialised to camera view bounding extents).

X,Y offsets, scaling and rotations would be applied to these starting UV coordinates.

A texture material would "stretch/fit" the extents of the stroke for local UV and "cookie cutut" for global UV. The gradient material would be scaled/cropped similarly.