css selector calculate specificity tool

[idoros]

This PR adds calcSpecificity exported function to @tokey/css-selector-parser that accepts selector AST and returns a tuple of specificity and an helper compareSpecificity function to compare 2 specificity values.

• base selectors: *, type, ::pseudo-element, .class, [attribute], :pseudo-class, #id, &
• inner most specific selector: :not(), :is(), :has()
• zero specificity: :where(), combinators, An+B...
• pseudo-class + most specific selector: :nth-child(), :nth-last-child(), :nth-of-type(), :nth-last-of-type()
• non native functional selectors ignore arguments specificity
• browser prefixes - no such prefixes for any special case
• immutable / mutable input type test
• inner AST input support: Selector | SelectorNode
• compareSpecificity function
• documentation

[barak007]

see comments