Utilize `string_view` initialization of `TfToken` in path parsing

[nvmkuruc]

Description of Change(s)

(Depends on #3053)

GetToken tries to minimize dynamic allocations during path parsing by utilizing a stack allocated char[32] that can be explicitly NULL-terminated. This optimization still involves a copy to the intermediate buffer and only works for short strings.

This changes GetToken to use the new std::string_view constructor for TfToken instead. When the components of the path already exist in the registry, no copies or allocations are required. We've seen performance gains of about 4-8% in a simple test case where all the path components already exist as tokens.

Fixes Issue(s)

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• [ ] I have verified that all unit tests pass with the proposed changes
• [x] I have submitted a signed Contributor License Agreement

[jesschimein]

Filed as internal issue #USD-9589

[jesschimein]

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