Implement getClassOrder instead of sortClassList

[RobinMalfait]

This PR implements a getClassOrder instead of sortClassList.

Had a conversation with @bradlc and while sorting in Tailwind itself works, it can happen that instead of placing unknown classes in the front that you want to put it in the back. This is an option that we can expose in the prettier-plugin-tailwindcss if we event want to do that. But if we want those options in Tailwind itself then we have to keep an options object into account or even more unknown complex scenarios.
So instead we will expose a getSortOrder that will return a list of tuples with the className and the order it appears in the final css when we generate it.

• Note: the order value is a bigint and the first value in the css will be the lowest number, the last value in the css will be the highest number. Those numbers are not per se consecutive.

Now the prettier-plugin-tailwindcss can sort the classes based on configuration settings in the plugin and using the information we expose via the getClassOrder .

When a class is passed to the function that doesn't exist, then the sort value will be set to null.

If we in the future want to change the sort algorithm internally, then we can expose the same list but maybe with different numbers as long as they stay in order.

Remaining questions:

• Is the name getSortOrder good, or do we prefer something like getClassOrder (similar to the already existing getClassList)? Renamed it to getClassOrder