Autodesk: Add DIFF_COMPARE_OPTIONS to pxr_register_test()

[erikaharrison-adsk]

Description of Change(s)

⚠ Branched off feature-hgi-vulkan

• Add DIFF_COMPARE_OPTIONS to pxr_register_test(), and always use diff in testWrapper.py
  • Windows fc doesn't support the options used by some tests, so we need to switch to diff if we want to enable these tests on Windows.
  • Add logic to find diff on Windows, working of the fact that git will most surely be installed, and it comes with it.

Link to proposal (if applicable)

• N/A

Fixes Issue(s)

• N/A

Checklist

[ ] I have created this PR based on the dev branch

[X] I have followed the coding conventions

[ ] I have added unit tests that exercise this functionality (Reference:
testing guidelines)

[X] I have verified that all unit tests pass with the proposed changes

[X] I have submitted a signed Contributor License Agreement (Reference:
Contributor License Agreement instructions)

[jesschimein]

Filed as internal issue #USD-10413

[jesschimein]

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