Allow promise-like objects as loadUtilsOnInit option

[MarcoGlauser]

Related to #1877
This solves the issue that angular can't load the utils script because zone.js wraps promises.

The utils loader currently does an instanceof check against the builtin Promise type. This doesn't work with wrapped promises, bluebird promises or other custom promises.

By wrapping the source() result in a Promise.reslove(), instead of the instanceof check, we're making sure that we're working with a promise.

I've added a specific testcase for a custom thenable that works with this patch.

[jackocnr]

Checking with @Mr0grog, who implemented this code. Any thoughts before I merge?

[Mr0grog]

@jackocnr This seems fine to me. 👍 The main thing worth considering is that this will also allow the loadUtilsOnInit function to return the utils module object directly instead of just as a promise. That is, you can now do:

intlTelInput(inputElement, {
  // No promises involved!
  loadUtilsOnInit: () => ({
    default: { /* Locally defined utils module, or a mock, or whatever here */ }
  })
});

But that flexibility might be useful! So I think this is probably a good change. (Side note: the function can technically return anything with this change, but we have code later [line 2168] to validate that it at least vaguely looks like a JS module object, so that should be OK.)

OTOH, if you want to keep requiring that this returns a thennable (the more generic form of a JS promise), then the right canonical check would be something like:

loadCall = source();
if (typeof loadCall?.then !== 'function') {
  // Throw an error (or maybe return a rejection instead)
}

…but like I said, I think the added flexibility in this change as-is is probably better.

[jackocnr]

Manually resolved conflicts and merged. Thank you so much. Released in v24.8.1.