D1705: Fix Grease Pencil Fill for Concave Shapes

Improve filling for concave shapes using a triangulation of the stroke.
The triangulation information is saved in an internal cache and only is
recalculated if the stroke changes.

The triangulation is not saved in .blend file.

Reviewers: aligorith

Maniphest Tasks: T47102

Differential Revision: https://developer.blender.org/D1705

release/scripts/startup/bl_ui/properties_grease_pencil_common.py

@@ -576,6 +576,7 @@ class GreasePencilDataPanel:
         col = split.column(align=True)
         col.prop(gpl, "line_width", slider=True)
         col.prop(gpl, "use_volumetric_strokes")
+        col.prop(gpl, "use_hq_fill")
 
         col = split.column(align=True)
         col.prop(gpl, "show_x_ray")