Improve support for `throw`.
Improve support for `throw`.

This ensures that `throw` used as an expression works correctly, that it communicates that it prefers not to be used that way, and that it cannot be implicitly returned.

alangpierce/decaffeinate,eventualbuddha/decaffeinate,alangpierce/decaffeinate,decaffeinate/decaffeinate,eventualbuddha/decaffeinate,decaffeinate/decaffeinate,alangpierce/decaffeinate