whatsnew: importlib deprecations.

This addresses issue #20199, if I got it right.  The deprecation and
replacement lists are based on the importlib documentation.
whatsnew: frozen package __path__; and min/max versionadded.
Issue #20484: Disable the 2 remaining "modules" tests in test_pydoc.

I'll look into re-enabling them in issue #20128.
whatsnew: Windows uses VirtualAlloc, --version goes to stdout.
whatsnew: PyStructSequence_InitType2, Victor's MemoryError fixes.

I'm documenting this new function, but I'm wondering if this will trigger
someone to think about whether or not this actually makes sense :)
whatsnew: os.path.ismount recognizes volumes mounted below root.
Reflow paragraph.
Issue #20641: Run custom actions with the NoImpersonate flag to support UAC.
Issue #20730: Fix typo reported by Claudiu Popa.
Merge with 3.3