Fixes CityOfDetroit/detroitmi#1112

[maxatdetroit]

Fixes CityofDetroit/detroitmi#1112

Using REMs (in conjunction with a statically set, small HTML element font-size) results in disproportionately small components on detroitmi.gov.

As discussed with @bankovic and @jedgar1mx , we're going to shift the UXDS to use EMs instead of REMs to allow the design system to have more independence and customization w.r.t. size.

This PR:

• Changes all uses of REM to EM in compiled CSS
• Creates a script to handle regenerating bootstrap and replacing uses of REM
• Adds warnings about manually editing compiled bootstrap and instructions to use the compilation script

Testing

Run the script locally:

√ ~/projects/uxds % ./scripts/compile_bootstrap.sh
Compiling bootstrap SASS...
Replacing REMs with EMs...
Formatting output...
src/shared/themed-bootstrap.css 715ms

Tested visually by viewing button components in storybook:

I'd like to test this on the detroitmi.gov site where the actual regression occurred, however my local instance is struggling to run due to memory constraints so I cannot test style changes locally. I considered trying to have the dev site use the style changes but that would require either packaging this change and bumping the version on dev or changing the dev site to use a local package both of which seemed overly cumbersome. @jedgar1mx would you be able to test this when creating the next package?

[jedgar1mx]

This fixes issues on detroitmi