Draft: Bug 40288+40299+28102 (Make sure we pick the exact same compile environment for Tor Browser builds)

This is still a draft.

Closes #40288 (closed), #40299 (closed), #28102

I was able to do macOS builds with this patch.

Using apt-transport-mirror with mmdebstrap requires two patches that I will submit upstream:

• https://gitlab.torproject.org/boklm/tor-browser-build/-/blob/89d46d069d6ccadcfad77ef1b8209dc215c76493/projects/mmdebstrap-image/fix-mirror+https-urls.patch
• https://gitlab.torproject.org/boklm/tor-browser-build/-/blob/89d46d069d6ccadcfad77ef1b8209dc215c76493/projects/mmdebstrap-image/fix-auxfiles-error.patch