This patch improves working with grease pencil layers in geometry nodes.
* Allow layers to have duplicate names in geometry nodes. In original data, unique names are enforced.
* This allows e.g. duplicating layers and then merging them by name in the end.
* It also resolves a big serial bottleneck when working with many grease pencil layers in geometry nodes. Enforcing unique names is inefficient.
* New `Merge Layers` node that can merge multiple layers by name or by a custom group id.
* Applying a grease pencil modifier now first merges all layers with the same name to ensure all names are unique.
Co-authored-by: Jacques Lucke <jacques@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/127873
53b9594ee2