Use venv for macOS when installation method is tgz

[jwnimmer-tri]

Is your feature request related to a problem? Please describe.

When installing a binary release of Drake on macOS using the tar.gz download installation method (aka from_binary), Drake currently runs a pip command:

drake/setup/mac/binary_distribution/install_prereqs.sh

Line 70 in 82999cb

pip3.12 install --break-system-packages -r "${BASH_SOURCE%/*}/requirements.txt"

Note that we are running the pip3.12 command from homebrew, which means that --break-system-packages is installing Drake's python dependencies system-wide. That is not a good idea for just to run software library someone just downloaded. They should be able to run Drake without polluting their system-wide homebrew python path.

We should ensure that users always run using some kind of virtual environment, and provide good docs/code in support of that.

Links to topical end-user documentation:

• https://drake.mit.edu/from_binary.html#use-as-a-python-library
• https://github.com/RobotLocomotion/drake-external-examples/tree/main/drake_cmake_installed#readme

Describe the solution you'd like

(1) Change anything and everything that's necessary (Drake's binary packages, Drake's install_prereqs scripts, Drake's documentation, DEE's code, DEE's documentation, etc) so that running a Drake tgz binary release on macOS does not pollute homebrew python.

(2) The binary_distribution/Brewfile must no longer cite numpy, but everything else there (gcc, [email protected], etc.) is satisfactory to leave alone. We still want to use Homebrew's CPython interpreter, just not any of its third-party Python libraries. Drake should always be running inside of a virtual environment.

(3) The binary_distribution/requirements.txt must not be installed system-wide, but rather inside of a virtual environment. The documentation at https://drake.mit.edu/from_binary.html#use-as-a-python-library already has a start on this, but isn't well-matched for macOS because python3 might not point to homebrew python. Simply changing the documentation would be a plausible solution, but I imagine that combining these two lines ...

python3 -m venv env --system-site-packages
env/share/drake/setup/install_prereqs

... into just a one-liner call to env/share/drake/setup/install_prereqs might be less brittle (so that the python details can be scripted, instead of copy-pasted from the docs).

(4) Any scripts that we provide should (as much as practical) give the user good error messages in case they make a mistake, e.g., accidentally using Apple Python, or accidentally trying to run pip into the /opt/homebrew tree, etc.

(5) Fix the documentation at https://github.com/RobotLocomotion/drake-external-examples/tree/main/drake_cmake_installed to promise support for macOS (and by implication then also operate correctly on both Ubuntu and macOS).

Describe alternatives you've considered

n/a

Additional context

This is a sub-task of the #8392 epic.