Adds the initial stage for the grease pencil 3.0 project.
This patch includes:
* New ID and new object type.
* New DNA structures.
* New drawing engine for grease pencil (gpencil-next).
* Tests for the new grease pencil data-type.
* A few operators for conversion, switching modes and (simple) drawing.
Exposed to the user:
* An experimental option to switch to the new grease pencil.
* This will switch the grease pencil render engine to gpencil-next which can only render the new object type.
Current grease pencil objects will no longer render.
* Changing this option currently requires a restart of blender (for the keymap to update).
* A conversion setting in the `Object` > `Convert To` operator.
* A drawing operator in `Draw Mode`.
Pull Request: https://projects.blender.org/blender/blender/pulls/106848
3aaacd6e30