feat: url publicPath and assetDir can be a function

[KingSora]

Good day!

I'm using rollup-plugin-styles with the rollup options preserveModules and preserveModulesRoot. In the resulting file structure I need to keep the original publicPath of the url asset and the asset path should also remain the same. To make this possible I've added the possibility to make the url publicPath and assetDir option a function which gives you the original paths and resolved paths and its up to the consumer whats returned.