macOS installer shell path management improvements

The macOS Python installers provided on python.org with each Python release have long provided a fairly primitive mechanism to ensure the newly-installed Python is available on the user's shell PATH. A postinstall script is run by default by the installer which attempts to modify the user's login shell's profile to add the Python framework's bin directory to the shell PATH. A copy of the script is also included by default in the /Applications/Python 3.x directory. There are a number of shortcomings with this approach. This issue is a placeholder for upcoming work in this area.

Linked PRs

• gh-137451
• gh-137452
• gh-137453