Add Directory.CreateTempSubdirectory

[eerhardt]

CreateTempSubdirectory will create a new uniquely named directory under the temp directory. This allows applications to write temporary files in a co-located directory.

Contributes to #72881

Note: I've decided not to implement the full approved API in #72881 because of the feedback on the File API. That will be added in a future PR.

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Issue Details

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CreateTempSubdirectory will create a new uniquely named directory under the temp directory. This allows applications to write temporary files in a co-located directory.

Contributes to #72881

Note: I've decided not to implement the full approved API in #72881 because of the feedback on the File API. That will be added in a future PR.

Author:	eerhardt
Assignees:	-
Labels:	area-System.IO, new-api-needs-documentation
Milestone:	-

[eerhardt]

I have responded to all existing feedback and pushed new changes. PTAL.