Use faster APIs to calculate paths at startup for Store packaged Python on Windows

[zooba]

These APIs were added in Windows 8, so we can safely backport.

[zooba]

The rough testing I did showed about 50% reduction in startup time (~450ms->250ms) in non-ideal circumstances, but the Windows devs I was working with said it seemed right. The numbers were pretty stable.

[zooba]

Okay, had to retract one of the major optimisations because it can be incorrect. That brings the improvement down to around 50ms, which is still worthwhile, but not as impressive.

However, users can at least override this perf impact by setting their own PYTHONUSERBASE env variable before launching.

[zooba]

It's possible we might be able to bring that optimisation back, looks like Windows covers the concerning edge cases for us. Still checking

[miss-islington]

Thanks @zooba for the PR 🌮🎉.. I'm working now to backport this PR to: 3.10, 3.11. 🐍🍒⛏🤖

[bedevere-bot]

GH-99733 is a backport of this pull request to the 3.11 branch.

[bedevere-bot]

GH-99734 is a backport of this pull request to the 3.10 branch.