Allow to process USD files to use relative paths when published

[BigRoy]

Changelog Description

This adds a publish plug-in that is able to remap all paths inside the USD layer to a relative path. As such, by doing so - this means that all published USD files will be using solely relative paths to other published paths.

Additional info

This could allow you to 'archive' your project or share the publishes (while maintaining the project's folder structure for the publishes) and share those files with others, allow them to load it - without having to remap anything and without using an asset resolver.

This uses UsdUtils.ModifyAssetPaths which has existed for at least six years in USD, see commit. So should be safe to use nowadays across the board, but for completeness it was added in USD 19.03 so this feature requires USD 19.03+

Example result when loading an asset back in:

The top non-relative path is just the 'path' I loaded into Houdini to check the file contents; so that not being relative is entirely correct.

This PR replaces ayon-core PR ynput/ayon-core#957

Testing notes:

1. Enable the plug-in in settings: ayon+settings://usd/publish/USDOutputProcessorRemapToRelativePaths/enabled. (It is disabled by default.)

2. Publishes from Maya and Houdini (and others that generate USD publishes with asset paths to other files) should now remap all asset paths to relative paths.

Tested:

• Houdini 20.5.320 on Windows
• Houdini x.x.x on Linux
• Maya 2025.2 on Windows

[ynbot]

Task linked: AY-6953 Publish USD files with relative paths to published file

[Lypsolon]

i did a simple test and it works.
i left a few comments on the implementation.

[Lypsolon]

works and while i don't like a few of the code quality solutions this works and is good to go.