fix checks for dynamic calls

[sigmundch]

Copied from John:

Consider:

class M {
 call(x,y) => x+y;
}
main() {
 M m = new M();
 print(m(1,2)); // works
 print(m(1,2,3)); // NoSuchMethodError at runtime. analyzer fails to catch
 print(m.call(1,2,3)); // analyzer correctly detects this
}

This blows up due to wrong number of arguments at runtime. However, I don't see any warnings or errors from dart2js or dartanalyzer.
DDC does not really catch this either. It is treated as dynamic dispatch and allowed, for some reason, even though we could've caught it statically.

Turns out that in checker.dart we only look at:

 if (type.isDynamic || type.isDartCoreFunction || type is! FunctionType) { ...

we should additionaly check if the type implements call and use it's type instead:

if (type is InterfaceType) {
  var callMethod = type.lookUpMethod("call", _current.library);
  if (callMethod != null) type = callMethod.type;
}
...

[jmesserly]

Yeah. Interesting to check some corner cases too, like obj.method(123). Where obj.method is a getter that returns an object with 'call' (I think that works, and we should be able to statically analyze it)

[vsmenon]

@leafpetersen is adding support for call methods. Not clear that's the only issue here.

[leafpetersen]

The analyzer seems to have fixed the issue that allows m(1, 2, 3). There is another bug which seems to cause it to treat the return types incorrectly (dartbug.com/23252). I have a CL pending which fixes the dynamic dispatch issue.