Calling a CanMap constructor creates a binding on __keys

[phillipskevin]

Calling a CanMap constructor inside of a getter sets up a binding on __keys for the created instance, which means that setting any property on that instance will cause the getter to rerun.

    import { CanMap } from "//unpkg.com/can@5/ecosystem.mjs";

    const OtherMap = CanMap.extend({});

    const MyMap = CanMap.extend({
      define: {
        foo: {
          get() {
            // calling this constructor sets up a binding on __keys
            return new OtherMap();
          }
        }
      }
    });

    var map = new MyMap();
    map.on('foo', () => {});
    map.attr('foo.bar', 'baz'); // triggers a `__keys` event on the `OtherMap`, which causes the `foo` getter to rerun
    console.log( map.attr('foo.bar') ); // -> undefined because `foo` is a new `OtherMap` instance

This happens because the constructor calls canReflect.assignDeep, which ends up calling getOwnEnumerableKeys, which creates this binding:

can-map/can-map.js

Line 659 in c1dca96

ObservationRecorder.add(this, '__keys');

I think this is a regression from 2.3, where this did not happen.