Rollup merge of #106216 - ChrisDenton:ps-go-faster, r=jyn514

Rollup merge of #106216 - ChrisDenton:ps-go-faster, r=jyn514

Powershell: Use `WaitForExit` instead of `-Wait`

Using the method `WaitForExit` instead of the parameter `-Wait` results in a notable speed up of the `x.ps1` script (~350ms, fairly consistently).

Results:
```
milliseconds before: 1127.7576
milliseconds after:   779.0467
```

I think there are opportunities for further speed up by calling `Get-Command` only once with the pattern `py*` then filtering the returned list.

But I'll leave that for another time (or someone else).

r? ``@jyn514``