#pattern is broken for client side validation

Problem/Motivation

After opening the field widget settings the browser reports:

Pattern attribute value ^(\d+(cm|mm|in|px|pt|pc|em|ex|ch|rem|vm|vh|vmin|vmax|\%)|element|style|resolve|auto|initial|inherit)$ is not a valid regular expression: Uncaught SyntaxError: Invalid regular expression: /^(\d+(cm|mm|in|px|pt|pc|em|ex|ch|rem|vm|vh|vmin|vmax|\%)|element|style|resolve|auto|initial|inherit)$/: Invalid escape

Proposed resolution

Fix the regex