Closes#13626.
Two follow-ups on top of the _hermes_home helper from @jerome-benoit's #12729:
1. Declare a [google] optional extra in pyproject.toml
(google-api-python-client, google-auth-oauthlib, google-auth-httplib2) and
include it in [all]. Packagers (Nix flake, Homebrew) now ship the deps by
default, so `setup.py --check` does not need to shell out to pip at
runtime — the imports succeed and install_deps() is never reached.
This fixes the Nix breakage where pip/ensurepip are stripped.
2. Add `from __future__ import annotations` to setup.py so the PEP 604
`str | None` annotation parses on Python 3.9 (macOS system python).
Previously system python3 SyntaxError'd before any code ran.
install_deps() error message now also points users at the extra instead of
just the raw pip command.