Extract the core of postcss-lit to allow other css-in-js syntaxes to be built

[43081j]

as per the title, we should extract the core of postcss-lit since it isn't actually specific to lit.

this would allow the community to build other css-in-js syntax support without having to reinvent the wheel.

this is just an issue to track my progress in doing so

cc @karlhorky @kutnickclose

related styled-components/styled-components#3897 stylelint/postcss-css-in-js#225

[karlhorky]

This is done already, right? Now that postcss-js-core is done? (And even the new syntax postcss-styled-components 🙌 )

Or do you want to leave it open until the PR below is merged?

• #42

[43081j]

it is done but i was waiting until i get chance to properly test and ship the postcss-lit branch basically.

to be honest it passes all tests and seems to work in my own projects, so i should probably just publish it and hope for the best 😂