Sponsor 131 - Phase 1 Roadmap for tor-browser-build

A potential roadmap, but of course edit to match reality

Add support for building browser packages without tor, tor-launcher, pts, etc

• Add base-browser targets to rbm.conf : #40522 (closed)
• update firefox project : #40499 (closed)
  • remove tor-launcher dependency for base-browser config
  • git hash to whatever 'base-browser' tag we come up with
• new base-browser package project analogous to current tor-browser project : #40500 (closed)
  • macOS -> dmg generation same as tor-browser
  • windows -> perhaps a more 'traditional' nsis installer (ie installing to %programfiles% rather than Desktop)
  • linux -> tar.gz is fine
  • swap out any assets icon with placeholders (this can literally be programmer art)
• (Optional) reproducibility; nice to have but if there are weird rabbit holes we can ignore until Phase 2
• Makefile updates : #40501 (closed)
  • base-browser alpha, nightly, testbuild build targets (so we can make easily make just base-browser packages)
  • add base-browser target to nightly-desktop target
• base-browser build target added to our nightly builds : tor-browser-bundle-testsuite#40046 (closed)