Enhance property exports and implement AST-based resolvers

[asamuzaK]

Description:

This PR improves the internal architecture of cssstyle by refining how property modules export their metadata and how values are resolved via AST types. It also ensures better compliance with Web Platform Tests and streamlines the value processing logic.

Key Changes:

• Property Name Exports: Each property module now explicitly exports its property name as module.exports.property. This replaces previously hardcoded strings (e.g., "background") with a more maintainable, reference-based approach for property names.
  • NOTE: Planning to apply this to normalize.js in a separate follow-up PR.
• New AST Resolvers in parsers.js: Added a set of helper functions (resolvers) that dispatch values to the appropriate parser based on their AST (Abstract Syntax Tree) type. This logic has been applied across the property files in lib/properties/*.js to streamline value processing.

Additional Improvements:

• Refactored Priority Calculation: As a related cleanup, the logic for determining the priority argument in property setters has been simplified and unified. This reduces code duplication and ensures consistent behavior across different properties.

Impact:

• Supersedes Refactor property descriptor logic #272: This PR covers the objectives of Refactor property descriptor logic #272 with a more robust implementation and should be considered its replacement.

Testing:

• Verified that npm test passes.
• Confirmed the fix for wpt:tuwpt css/cssom/serialize-whitespace.html.

[domenic]

All of this looks good except I don't understand the last commit. Can you expand on what it fixes and give it a better commit title/message?

[asamuzaK]

getPropertyDescriptor() is a function that returns generic getters and setters for properties not included in properties/*.js.
In the original implementation, the setter only performed a simple process of parsing the CSS input and setting it as-is. In this PR, I have updated it to handle properties more appropriately (at least to a minimum extent) by utilizing AST_TYPES.

I had already submitted the changes to getPropertyDescriptor() as a separate PR #272, but since both properties/*.js and utils/propertyDescriptor.js now share the same logic of importing and using AST_TYPES, I decided to put them into this single PR.

[domenic]

I've updated the commit description to include that and will merge after CI finishes.

As always, let me know when is a good time for a new release!