feat(polyfill): Move querySelector polyfill from jitsi-meet and migrate to TypeScript

[hristoterezov]

Summary

Moves the querySelector/querySelectorAll polyfill from jitsi-meet repository to @jitsi/js-utils for better reusability across Jitsi projects. Converts the implementation to TypeScript and adds robust support for Document, DocumentFragment, and Element node types.

Changes

• Moved polyfill from jitsi-meet to @jitsi/js-utils for shared usage
• Migrated to TypeScript with full type safety and proper interfaces
• Removed all unsafe type assertions using function overload pattern with boolean parameters
• Added proper Node type support:
  • _getSearchElements() helper handles Document/DocumentFragment/Element nodes
  • querySelector/querySelectorAll check root elements before searching descendants
  • Internal functions simplified to only accept Element type
• Added try-catch for complex selectors when checking root element matches
• Updated tsconfig.json to include the new TypeScript polyfill
• Clean overload pattern for all internal functions (no as any assertions)

Benefits

• ✅ Shared polyfill reduces code duplication across Jitsi projects
• ✅ TypeScript provides better type safety and IDE support
• ✅ document.querySelector('html') correctly finds the root element
• ✅ documentFragment.querySelector() works properly
• ✅ XML documents with any root element name are supported
• ✅ Complex selectors like 'body > div' work correctly with Document nodes
• ✅ Zero unsafe type assertions in the codebase

Test Plan

• Run npm run build - TypeScript compilation passes
• Run npm run lint - ESLint passes with no errors
• Test with jitsi-meet integration
• Verify polyfill works with Document, DocumentFragment, and Element nodes
• Test with simple selectors ('html', 'body', 'div')
• Test with complex selectors ('body > div', :scope > span')