usdedit: Handle spaces in the file path to executables

[medakk]

Description of Change(s)

Correctly handle the case when the path to the editor has a space in it. This can often happen because of paths starting with C:\Program Files\...

Fixes Issue(s)

• 2757

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

Three failures, but they look unrelated?

        453 - testUsdZipFile (Failed)
        711 - testUsdviewNavigationKeys (Failed)
        727 - testUsdResolverExample (Failed)

• [X] I have submitted a signed Contributor License Agreement

[jesschimein]

Filed as internal issue #USD-9548

[jesschimein]

/AzurePipelines run

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[jesschimein]

/AzurePipelines run

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Azure Pipelines successfully started running 1 pipeline(s).