What problem does this solve or what need does it fill?

We have Mesh::insert_attribute and Mesh::remove_attribute.

But for indices we have Mesh::remove_indices (added in #11733) and Mesh::set_indices which accepts Option. It's inconsistent with the attributes API.

What solution would you like?

I would suggest to make Mesh::set_indices similar to Mesh::insert_attribute, i.e. pass the value instead of Option.

Ping @solis-lumine-vorago since he may be interested in it.