CSS Variables as colorpicker inputs

[stuartromanek]

Summary

• Adds the capability to supply CSS variable names as a selectable color swatches in the AposColor input type

Testbed

• ✅ Passing

What are the specific steps to test this change?

• Checkout public-demo#color-var-demo
• The Global schema is configured with a Color Picker Test field. See that all the swatches are populated. Use them. Change them. Make sure they act right. Make sure the setting persists.
• Rich Text widgets on the homepage are also configured to use the color picker via TipTap. Set a piece of text to a color using a variable. Make sure the setting persists.

What kind of change does this PR introduce?

(Check at least one)

• Bug fix
• New feature
• Refactor
• Documentation
• Build-related changes
• Other

[BoDonkey]

LGTM - tests fine and code is sane.