feat(directives): support theme() function

[Dunqing]

close: #982
Related docs: https://windicss.org/features/directives.html#theme

• Improved implementation of directives to support easier addition of directives
• Supports the theme() function directive, which allows multiple parameters.

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[Dunqing]

There seems to be some problems with ci testing, the last few ci jobs have failed.

[antfu]

Should we throw on none-exist utils?

[Dunqing]

Should we throw on none-exist utils?

I think it would be better to keep the non-existent utils to better troubleshoot the problem.

[antfu]

The multiple parameters feature feels a bit confusing to me, since ppl might expect to use space or comma for the conjunction base on their needs. I think either Tailwind or Windi support that usage currently, I'd prefer to not have it for the initial implementation (we could discuss in other issue)

I will work on this PR directly and handle the rest.

[Dunqing]

The multiple parameters feature feels a bit confusing to me, since ppl might expect to use space or comma for the conjunction base on their needs. I think either Tailwind or Windi support that usage currently, I'd prefer to not have it for the initial implementation (we could discuss in other issue)

Ok, I didn't notice that they don't support multiple parameters.