W-22619604 ISML support in vs extension

[charithaT07]

Summary

Brief description of what this PR does.

PR Summary

This PR adds comprehensive ISML language support to the VS Code extension, moving toward Prophet-level parity for authoring, navigation, diagnostics, and semantic intelligence.

What’s Added

ISML language assets

• Added language/isml/isml.tmLanguage.json
• Added language/isml/isml.snippets.json
• Added language/isml/language-configuration.json

ISML language feature module (src/isml/*)

• Diagnostics and ISML-specific quick fixes
• Rich hover docs for ISML tags
• Hierarchical document symbols (Outline)
• Folding range support (gutter expand/collapse arrows)
• Tag matching + linked editing
• Template document links for template="..."
• Semantic completions / go-to-definition / references for:
  • Resource.msg / Resource.msgf
  • URLUtils.*
  • res.render(...)
  • require(...)
• Scanner-based tokenization via vscode-html-languageservice

Extension wiring/config updates

• Registered all ISML providers in extension activation flow
• Updated command contributions for ISML actions
• Enabled ISML editor defaults (e.g., linked editing)
• Updated dependency/workspace metadata as needed

Test coverage

• Added/expanded tests in src/test/isml.test.ts for:
  • diagnostics + quick fixes
  • semantic completion/definition/reference flows
  • tag matching + linked editing
  • symbols + folding
  • template link detection/resolution

Why

ISML authoring support previously lacked robust structural + semantic intelligence.
This PR improves correctness, discoverability, and productivity for ISML developers directly in VS Code.

Validation

• Local tests pass for VS extension suite, including new ISML tests.
• Changes are scoped to ISML language support and related extension/test/config wiring.

Scope

• Primary package: packages/b2c-vs-extension
• Includes source, language assets, tests, and package/workspace config updates required for ISML support.

Testing

How was this tested?

Dependencies

• No net-new third-party dependencies were added
• If net-new third-party dependencies were added, rationale/discussion is included and 3pl-approved is set by a maintainer

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• Tests pass (pnpm test)
• Code is formatted (pnpm run format)