Wrong version of python launched in `sim_vehicule.py` after installation with `environment_install` tool on Windows

Bug report

Issue details

After running the environment_install tool for Windows install-prereqs-windows.ps1, I follow the Copter SITL/MAVProxy Tutorial and running this command give me an error :

$ ../Tools/autotest/sim_vehicle.py --map --console
Traceback (most recent call last):
  File "/cygdrive/c/Users/jmaitr03/Documents/Github/ardupilot/ArduCopter/../Tools/autotest/sim_vehicle.py", line 31, in <module>
    from pysim import util
  File "/cygdrive/c/Users/jmaitr03/Documents/Github/ardupilot/Tools/autotest/pysim/util.py", line 19, in <module>
    import pexpect
ModuleNotFoundError: No module named 'pexpect'

I found that in the sim_vehicule.py script, the shebang is wrong because it says :

#!/usr/bin/env python3

python3 is a symbolic link to /etc/alternatives/python3 which is not python 3.7 (but python 3.9)

In the install-prereqs-windows.ps1 script, a symbolic link are made to python3.7 but with the name python and not python3 :

Start-Process -wait -FilePath "C:\cygwin64\bin\bash" -ArgumentList "--login -i -c 'ln -sf /usr/bin/python3.7 /usr/bin/python'"
Start-Process -wait -FilePath "C:\cygwin64\bin\bash" -ArgumentList "--login -i -c 'ln -sf /usr/bin/pip3.7 /usr/bin/pip'"

This misconfiguration causes the error shown above.

Version
Ardupilot-git

Platform
[X] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

Hardware type
Windows

Start with Tools/autotest/sim_vehicle.py and install-prereqs-windows.ps1, then reproduce the documented Windows SITL command and inspect which Python executable it selects. Done means the command uses the Python version installed by the Windows prerequisites and imports pexpect without the reported ModuleNotFoundError.