Currently attribute names are often added to a hash map that doesn't
maintain the original order. This is convenient for developers but it's
better for users if attributes aren't arbitrarily reordered. Instead,
use `VectorSet` which gives the benefit of a hash map but maintains the
insertion order. The main downside is the loss of O(1) removal which we
benefited from in a few cases. I used string comparison instead for now.
Fixes#144491, #122994
Pull Request: https://projects.blender.org/blender/blender/pulls/145668
5418f0bc68