Add test to reproduce multi-threading issue of computing extent and relationship

[roggiezhang-nv]

Description of Change(s)

We found a very strange behavior that ComputeExtent along with GetForwardedTargets in a multi-threading way would influence the behavior of getting material binding with API UsdRelationship::GetForwardedTargets. See the changes of this PR about the test to reproduce this. In this test, it's trying to traverse the whole stage with multi-threads. All operations are supposed to be read-only to the stage, and the test should be successful. However, it fails unexpectedly sometimes. Adding TfRegistryManager::GetInstance().SubscribeTo<UsdGeomBoundable>(); to the first line of main() will pass the test, which we still have no idea why.

You need to run the test with --repeat until-fail:1000 to increase the possibility of failure.

Fixes Issue(s)

#3529

Checklist

[x] 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)

[ ] 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)

[roggiezhang-nv]

@nvmkuruc for vis.

[nvmkuruc]

It was a little harder to reproduce on Linux, but I was able to reproduce with --repeat-until-fail 10000.

[jesschimein]

Filed as internal issue #USD-10665

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[jesschimein]

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