GPencil: Refactor of Draw Engine, Vertex Paint and all internal functions

This commit is a full refactor of the grease pencil modules including Draw Engine, Modifiers, VFX, depsgraph update, improvements in operators and conversion of Sculpt and Weight paint tools to real brushes.

Also, a huge code cleanup has been done at all levels.

Thanks to @fclem for his work and yo @pepeland and @mendio for the testing and help in the development.

Differential Revision: https://developer.blender.org/D6293

release/scripts/startup/bl_operators/presets.py

@@ -642,10 +642,7 @@ class AddPresetGpencilBrush(AddPresetBase, Operator):
         "brush.smooth_stroke_factor",
         "settings.pen_smooth_factor",
         "settings.pen_smooth_steps",
-        "settings.pen_thick_smooth_factor",
-        "settings.pen_thick_smooth_steps",
         "settings.pen_subdivision_steps",
-        "settings.random_subdiv",
         "settings.use_settings_random",
         "settings.random_pressure",
         "settings.random_strength",
@@ -675,8 +672,6 @@ class AddPresetGpencilMaterial(AddPresetBase, Operator):
         "gpcolor.color",
         "gpcolor.stroke_image",
         "gpcolor.pixel_size",
-        "gpcolor.use_stroke_pattern",
-        "gpcolor.use_stroke_texture_mix",
         "gpcolor.mix_stroke_factor",
         "gpcolor.alignment_mode",
         "gpcolor.fill_style",
@@ -686,18 +681,11 @@ class AddPresetGpencilMaterial(AddPresetBase, Operator):
         "gpcolor.mix_color",
         "gpcolor.mix_factor",
         "gpcolor.flip",
-        "gpcolor.pattern_shift",
-        "gpcolor.pattern_scale",
-        "gpcolor.pattern_radius",
-        "gpcolor.pattern_angle",
-        "gpcolor.pattern_gridsize",
-        "gpcolor.use_fill_pattern",
         "gpcolor.texture_offset",
         "gpcolor.texture_scale",
         "gpcolor.texture_angle",
         "gpcolor.texture_opacity",
         "gpcolor.texture_clamp",
-        "gpcolor.use_fill_texture_mix",
         "gpcolor.mix_factor",
         "gpcolor.show_stroke",
         "gpcolor.show_fill",