Colorize CSS property value like `css--fontify-region'

Colorize CSS property value like `css--fontify-region'

If the value of a property is text representing a CSS color,
it will be fontified such that its background is the color
itself. 'php-ts-mode-css-fontify-colors' can be used to
disable this behaviour.
* lisp/progmodes/php-ts-mode.el (php-ts-mode-css-fontify-colors):
New custom var.
* lisp/progmodes/php-ts-mode.el (php-ts-mode--colorize-css-value):
New function.
* lisp/progmodes/php-ts-mode.el (php-ts-mode): Use the new
function.  (Bug#71724)

(cherry picked from commit 2f1c882a16e5e5215da039af1b4c4a8f569db1a1)