mkvenv: add console script entry point generation

mkvenv: add console script entry point generation

When creating a virtual environment that inherits system packages,
script entry points (like "meson", "sphinx-build", etc) are not
re-generated with the correct shebang. When you are *inside* of the
venv, this is not a problem, but if you are *outside* of it, you will
not have a script that engages the virtual environment appropriately.

Add a mechanism that generates new entry points for pre-existing
packages so that we can use these scripts to run "meson",
"sphinx-build", "pip", unambiguously inside the venv.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20230511035435.734312-9-jsnow@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>