Move the mask_random function to BLI_index_mask.hh, so it can be shared between curves, grease pencil and point cloud.
Copied/inspired by the curves select code.
Pull Request: https://projects.blender.org/blender/blender/pulls/134624
Though "Point Cloud" written as two words is technically correct and should be used in the UI, as one word it's typically easier to write and parse when reading. We had a mix of both before this patch, so better to unify this as well.
This commit also renames the editor/intern/ files to remove pointcloud_ prefix.
point_cloud was only preserved on the user facing strings:
* is_type_point_cloud
* use_new_point_cloud_type
Pull Request: https://projects.blender.org/blender/blender/pulls/134803
