gh-128397: Makes _delete attribute from TemporaryDirectory public

[Prtm2110]

Fixes: #128397
As mentioned it the issue this PR makes _delete attribute of TemporaryDirectory public, I will write tests and add change log accordingly.

• Issue: Promote _delete member of TemporaryDirectory to delete #128397

[cpython-cla-bot]

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[Prtm2110]

Hello, @graingert (I’m not sure if tagging you is appropriate here), but could you please provide a review of this?

[graingert]

You'll need to write some test cases for mutating delete outside the constructor, and some docs changes.

Please also write a test case for what happens when the object is created with delete=True, changed to delete=False and then garbage collected