Document data types for functional utilities

[c-harding]

Source: tailwindlabs/tailwindcss#16617

The list of supported data types is color, length, percentage, ratio, number, integer, url, position, bg-size, line-width, image, family-name, generic-name, absolute-size, relative-size, angle, vector.

This should be added to the page https://tailwindcss.com/docs/adding-custom-styles#functional-utilities: I was confused that I couldn’t get custom-ident to work.

The same page, higher up, links to MDN without a note about only certain types being supported.