feat: Custom property value replacement in lexer.matchProperty

[nzakas]

This change gives us the ability to pass in substitute values for variables when validating a property. The idea is that ESLint could keep track of the last value for any given custom property and pass that into lexer.matchProperty() so that we can actually validate property values containing var() (right now CSSTree just throws an error, which we swallow in the ESLint rule).

Ported from csstree#321
This pull request introduces changes to the lexer to support matching CSS properties that use the var() function. The changes include adding tests for var() handling and modifying the lexer to replace var() tokens with their corresponding values.

Enhancements to var() handling:

• lib/__tests/lexer-match-property.js: Added tests to ensure var() is correctly matched when variable values are provided and returns an error when not supported.

Lexer modifications:

• lib/lexer/Lexer.js: Added the replaceVarTokens function to handle the replacement of var() tokens with their corresponding values. Modified matchSyntax, matchDeclaration, and matchProperty functions to support options for variable values. [1] [2] [3]

[nzakas]

Can't quite figure out how to get the correct information into the match error. 🤔