properly retain closures used via js-interop

[sigmundch]

We seem to have a bug in CPS IR related to passing closures through js-interop. It might be that we don't mark a closure as escaped when we pass it to a js-interop API, or that we don't recognize that all closures could be invoked via JsObject.callMethod.

This only happens if the closure signature is not seen anywhere else in the Dart code. For example, the closure in the repro below is the only closure with 11 arguments. If we change it to take 4 or less arguments, then the closure is available and the program runs correctly.

Here is simplified repro, derived from the test in tests/html/js_test/Dart_functions:

import 'dart:js';

main() {
  context['f'] =
    (a, b, c, d, e, f, g, h, i, j) => print('$a $b $c $d $e $f $g $h $i $j');
  context.callMethod('f',
      ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J']);
}

This prints A B C D E F G H I J when compiled with SSA, but throws the following error with CPS IR:

Receiver: Closure 'main_closure'
Arguments: ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"]
          throw e;
          ^
NoSuchMethodError: method not found: 'call'
Receiver: Closure 'main_closure'
Arguments: ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"]
    at dart.wrapException (cps.js:1847:18)
    at main_closure.dart.Object.noSuchMethod$1 (cps.js:4196:17)
    at J.noSuchMethod$1$ (cps.js:5210:39)
    at dart.Primitives_functionNoSuchMethod (cps.js:1785:9)
    at dart.Primitives_applyFunctionWithPositionalArguments (cps.js:1808:20)
    at dart._callDartFunction (cps.js:4650:31)
    at cps.js:4632:18
    at JsObject.dart.JsObject.callMethod$2 (cps.js:4769:44)
    at dart.main (cps.js:5051:10)
    at _IsolateContext.dart._IsolateContext.eval$1 (cps.js:1054:27)

Inspecting the output shows that the CPS IR has tree-shaken the call method of the closure.

[rakudrama]

Obsolete