selector-resolve-nested

[romainmenke]

This is the same algorithm as can be found in : #1140

Publishing it as a separate package allows others to make use of the same logic.
At this time this would be mainly Stylelint.

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Changes from the version in postcss-nesting

• arguments and return are postcss-selector-parser Root nodes, not strings
• a lot more tests (easier to have better coverage when this is a JS lib and not a PostCSS plugin)
• fixed some bugs

This package should also be used in an updated version of postcss-nesting

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The name is a bit awkward but I wanted a parallel with @csstools/selector-specificity.