- Move emscripten download into its own script
- Refactor the common "CI choice" prompt into its own file.
- Move the content of `build/common/ci-common.sh` to the
"CI choice" script.
- Mention the get-emscripten.sh script in BUILDING.md
- move CI only prerequisites to github actions
- Add linux, mac prereq actions
- Add an action for indicating dependency versions
- Move ninja installation into its own script
- Added an extra README file detailing what the scripts are for
- The scripts now display a warning and a prompt before requiring user confirmation to continue
- The system install commands are only executed in CI environments (ninja and cmake being installed as root without checking for the environment was a leftover from a previous non-GitHub based CI setup)
