Mesh insert indices

[lynn-lumen]

Objective

• Fixes Turn Mesh::set_indices into Mesh::insert_indices #11740

Solution

• Turned Mesh::set_indices into Mesh::insert_indices and added related methods for completeness.

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Changelog

• Replaced Mesh::set_indices(indices: Option<Indices>) with Mesh::insert_indices(indices: Indices)
• Replaced Mesh::with_indices(indices: Option<Indices>) with Mesh::with_inserted_indices(indices: Indices) and Mesh::with_removed_indices() mirroring the API for inserting / removing attributes.
• Updated the examples and internal uses of the APIs described above.

Migration Guide

• Use Mesh::insert_indices or Mesh::with_inserted_indices instead of Mesh::set_indices / Mesh::with_indices.
• If you have passed None to Mesh::set_indices or Mesh::with_indices you should use Mesh::remove_indices or Mesh::with_removed_indices instead.

[lynn-lumen]

I'm not sure about the naming of Mesh::with_removed_indices. Would Mesh::without_indices be better?

[IceSentry]

I personally prefer without_indices, but also, I'd prefer having with_indices and with_attribute. The _inserted_ part seems redundant to me.

But that's just personal preference, the current state of the PR LGTM

[alice-i-cecile]

Looks like this needs a bit of clean up: CI errors look real.

[mockersf]

new users of the renamed apis have been added to main, they need to be updated too

[lynn-lumen]

new users of the renamed apis have been added to main, they need to be updated too

Should be good to go now