The side effect of this bug was that venv environments directly
used the main interpreter instead of the intermediate stub executable,
which can cause problems when a script uses system APIs that
require the use of an application bundle.
This defines VPATH differently in PGO instrumentation builds, to account for a different default output directory. It also adds sys._vpath on Windows to make the value available to sysconfig so that it can be used in tests.
The getpath.py file is frozen at build time and executed as code over a namespace. It is never imported, nor is it meant to be importable or reusable. However, it should be easier to read, modify, and patch than the previous code.
This commit attempts to preserve every previously tested quirk, but these may be changed in the future to better align platforms.
