Modernize Problem Block JavaScript

[irtazaakram]

Description:

Refactor all Problem Block–related JavaScript files to modern ES6+ syntax.
This removes legacy RequireJS patterns and aligns code style with xblocks-contrib/problem.

Acceptance Criteria:

• All JS modules use ES6+ syntax
• No RequireJS dependencies remain
• All Karma and unit tests pass

[farhan]

As per discussion in the grooming, it's an optimization rather than the task that covers with in Problem XBlock extraction.
So moving it to the backlog to pick it up in the future.