This makes it so GPv3 objects are rendered using the current grease pencil render engine.
A new `gpencil_next` engine was added at the beginning of the project, but it couldn't
be finished in time. This commit removes the `gpencil_next` engine as it is no longer
used. The current status of the new engine been pushed to the `gpencil-next` branch on
the `blender` repository.
Note: Onion skinning is not supported yet. This work will be done in a separate PR.
Fixes#115467 and #116347.
Pull Request: https://projects.blender.org/blender/blender/pulls/118664
a3243172bf