[js-api-parser] Refactor Js parser: phase0

[KarishmaGhiya]

This PR does the following tasks from issue #12981

Create TokenGenerator interface
Create generator registry (src/tokenGenerators/index.ts)
Integrate into buildMemberLineTokens with fallback
Implement Enum generator

[Copilot]

Pull Request Overview

This PR introduces a refactoring of the JavaScript API parser by implementing a plugin-based token generation system. It creates an ITokenGenerator interface, a generator registry, and implements the first concrete generator for enums.

Key changes:

• Introduced ITokenGenerator interface for extensible token generation
• Created a registry-based system for managing token generators
• Implemented enum token generator as the first concrete generator

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
tools/apiview/parsers/js-api-parser/src/tokenGenerators/interfaces.ts	Defines the ITokenGenerator interface with isValid and generate methods
tools/apiview/parsers/js-api-parser/src/tokenGenerators/index.ts	Exports the generator registry array containing registered token generators
tools/apiview/parsers/js-api-parser/src/tokenGenerators/enum.ts	Implements the enum token generator (contains structural issues)
tools/apiview/parsers/js-api-parser/src/generate.ts	Integrates the generator registry into buildMemberLineTokens with fallback logic

[maorleger]

Coming along nicely and I love the fast turnaround - we need to add some tests though, this is our chance to add nice test coverage (doesn't have to test everything but just the important stuff) to avoid regressions in the future 👍

[KarishmaGhiya]

@jeremymeng @maorleger I addressed some of the comments. Can you review again? I added tests too.

[maorleger]