add support for roledefinitions function

[polatengin]

PR Summary

• Add support for the Bicep-emitted roleDefinitions(...) ARM expression function.
• Return the expected id and roleDefinitionId fields so expressions like roleDefinitions('Contributor').id can expand correctly.
• Add focused unit coverage for direct function evaluation and expression-builder property access.
• Update the changelog.

Fixes #3776

PR Checklist

• PR has a meaningful title
• Summarized changes
• Change is not breaking
• This PR is ready to merge and is not Work in Progress
• Rule changes
  • Unit tests created/ updated
  • Rule documentation created/ updated
  • Link to a filed issue
  • Change log has been updated with change under unreleased section
• Other code changes
  • Unit tests created/ updated
  • Link to a filed issue
  • Change log has been updated with change under unreleased section