[compiler] Fix invariant error for optional chaining in try/catch

Optional chaining and other value blocks within try/catch blocks were throwing an Invariant error ("Unexpected terminal in optional") instead of the expected Todo error. This caused hard failures instead of graceful bailouts.

The issue occurred because DropManualMemoization and ValidateExhaustiveDependencies ran before BuildReactiveFunction, and encountered `maybe-throw` terminals in their switch statements without a handler, falling through to the invariant case.

Fixed by adding explicit `maybe-throw` cases in both files that throw the proper Todo error with the message "Support value blocks (conditional, logical, optional chaining, etc) within a try/catch statement".

Also renamed the existing bug test to reflect it's now correctly handled:
- error.bug-invariant-unexpected-terminal-in-optional → error.todo-optional-chaining-within-try-catch

Closes #35570