Make use of USD's new UTF-8 support to allow our import/export code to
accept and generate appropriate USD files. This has been a long standing
shortcoming since USD's introduction, with incomplete and complicated
DCC-specific workarounds often attempted.
Summary of changes
- Export gets a new "Allow Unicode" option defaulting to "false". The
new Unicode USD files are not backward compatible. DCCs using older
versions of USD (before 24.03) will not be able to load such files so
we want to provide this as an opt-in option for now.
- Every location which used to call either `USDHierarchyIterator::make_valid_name`
or `pxr::TfMakeValidIdentifier` will now go through a new `make_safe_name`
API instead
- Export code is responsible for passing in the `allow_unicode` option
- Import code will always pass in `true` meaning Blender will happily
accept both existing and new Unicode USD files
Strangely, USD does not provide a convenient way of making valid UTF-8
identifiers and they left their old API unchanged. We had to roll our
own per their advice: https://forum.aousd.org/t/how-to-make-a-unicode-identifier-valid/1435
Pull Request: https://projects.blender.org/blender/blender/pulls/122471
9ad2c7df0b