Implementation of the GPv2 Fill tool in Grease Pencil 3. This tool creates new strokes where the user clicks, by rendering strokes into an image and then performing flood-fill and boundary search operations. This is a minimal first part, several features of the GPv2 tool are still missing (gap filling methods, smoothing, dilate/erode). Co-authored-by: Falk David <falk@blender.org> Pull Request: https://projects.blender.org/blender/blender/pulls/120693