Fix resource leak in hdSt

[dgovil]

Description of Change(s)

Garbage collect the texture handle registry and resource registry to prevent memory leaks.

Submitting on behalf of Maddy Adams

• [X] 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-9643

[jesschimein]

/AzurePipelines run

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