fix: preserve model materials across source reimport

[Kreblc3428]

PR Details

Fixes model material assignments becoming misaligned or losing references when updating a model from source after materials are removed and later restored.

The importer now aligns saved materials to the current source material order by name, while the editor reconnects genuinely reintroduced material slots to an existing same-named material asset.

Tested with the reproduction from #3363, including repeated v1 ? v2 ? v1 updates, multiple material removals, manual overrides, save/reopen, and running the editor.

Developed with assistance from ChatGPT using GPT-5.6 Sol. The final changes were reviewed and tested before submission.

Related Issue

Fixes #3363

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have built and run the editor to try this change out.

[Kryptos-FR]

This kind of changes needs new tests to cover that specific scenario.

[xen2]

FYI, I took a quick look at the failing tests and it seems to be AnimatedModel rendering all white: