Close for-of iterator when the loop body throws

[raskad]

Currently the iterator used in a for-of loop is not closed when the loop body throws. This PR fixes that by widening the scope of an exception handler that was already in place for some of the for-of assignment code paths.

To make this work I had to adjust the iterator close opcodes somewhat. The reason is that we may run into a situation when we attempt to close an iterator two times. See the following example:

var iterable = {};
iterable[Symbol.iterator] = function() {
  return {
    next: function() {
      return { done: false, value: null };
    },
    return: function() {
      throw "iter-close-error";
    }
  };
};

function f() {
  for (var x of iterable) {
    return;
  }
}
f();

In this example we close the iterator when we return from f inside of the loop body. The iterator close code is injected during the compilation of the return statement. The problem is that if the iterable.return function throws, like in the example, we start running the exception handler code that also attempts to close the iterator. To avoid this I adjusted the iterator close opcodes.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	50,268	50,268	0
Passed	42,769	42,771	+2
Ignored	1,391	1,391	0
Failed	6,108	6,106	-2
Panics	0	0	0
Conformance	85.08%	85.09%	+0.00%

Fixed tests (2):

test/language/statements/for-of/generator-close-via-throw.js (previously Failed)
test/language/statements/for-of/iterator-close-via-throw.js (previously Failed)

[HalidOdat]

Nice catch! :)