New color-contrast-enhanced rule (WCAG AAA)

[WilcoFiers]

We're increasingly starting to see folks ask for AAA tests. One rule we could easily add is a color-contrast-enhanced rule, which uses 7:1 contrast minimum for regular text, and 4.5:1 for large and bold text. See: https://www.w3.org/TR/WCAG21/#contrast-enhanced

This rule will be a copy of the existing color-contrast rule and check, using different check option defaults.

This rule will have to be off by default. Whether or not we do this for all AAA rules is yet to be decided. Currently the only AAA rule we have is on by default, but for something like color-contrast, it's probably not reasonable to keep it on.

[dan-tripp]

I'll try to fix this.

[WilcoFiers]

Sure thing, go for it.

[padmavemulapati]

Validated with the latest develop branch code base,
failing for the ratio:
`

and
Passing for the ratio: