Add parser support for explicit resource management (using/await using)

[abhinavs1920]

This Pull Request fixes/closes #4445

This PR introduces the parser foundation for the TC39 Explicit Resource Management proposal. It’s an initial step and does not yet include runtime support, which will be added gradually in future commits. Because this is a large feature, it will be developed over multiple commits.

It focuses on parsing support for using and await using, along with proper validation, AST integration, and test coverage. Runtime behavior is intentionally not included yet, using declarations are currently compiled as regular lexical bindings, with clear TODOs marking the follow-up work.

All existing parser tests continue to pass, and 5 new tests have been added for the new syntax. An example script and a short implementation roadmap are included to make future work straightforward.

This is the first step of a larger feature and is designed to be safe, incremental, and easy to review. Runtime disposal logic and related built-ins will be added in further commits of my work.

Thanks for reviewing!

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,862	52,862	0
Passed	49,472	49,472	0
Ignored	2,249	2,249	0
Failed	1,141	1,141	0
Panics	0	0	0
Conformance	93.59%	93.59%	0.00%