Previously, the modifier name was used to identify it in a compute context or
viewer path. Using `ModifierData.persistent_uid` (which was only introduced
later) has two main benefits: * It is stable even when the modifier name
changes. * It's cheaper and easier to work with since it's just an integer
instead of a string.
Note: Pinned viewer nodes will need to be re-pinned after the change.
Pull Request: https://projects.blender.org/blender/blender/pulls/138864
c77b93f49d