[rtext] Add support for Em Box font size metric (Supersedes #5949) - #6008

The following taps are not trusted: aws/tap Homebrew is currently ignoring formulae, casks and commands from these taps because tap trust is required. Untap them with: brew untap aws/tap Trust specific formulae, casks and commands with: brew trust --formula <user>/<tap>/<formula> brew trust --cask <user>/<tap>/<cask> brew trust --command <user>/<tap>/<command> Whole-tap trust is broader and includes all current and future formulae, casks and commands from the listed taps. Trust whole taps with: brew trust aws/tap To disable trust checks: export HOMEBREW_NO_REQUIRE_TAP_TRUST=1 This is not recommended and will be removed in a later release. For more information, see: https://docs.brew.sh/Tap-Trust