Limit QuickView to literal color names in some languages

For #6836.
Limits QuickView to only literal color names in JS (including JSON), PHP and CoffeeScript.
Includes Unit tests and one new test file.
`TokenUtils.getModeAt()` is not a cheap method to call, so we need to minimize the number of times it is called. Until we add support for inline css in style attributes, then it's safe to assume that entire line has same mode, so only need to check it once per line. It's simpler to just pass in `mode` instead of both `editor` and `pos`.