Fix errors with instanceof checks for custom objects.

[nerrad]

Problem this Pull Request solves

@tn3rb reported a bug with building an instance of BaseEntity using the money value objects. Doing something like this:

const money = new eejs.valueObjects.Money( 0, eejs.valueObjects.SiteCurrency );
const price = await wp.data.dispatch( 'eventespresso/core' ).createEntity( 'price', { PRT_ID: 2, PRC_name: '', PRC_desc: '', PRC_amount: money, PRC_order: 0 } );

...produced the following error:

Uncaught (in promise) TypeError: Instance of Money required
    at assertMoney (money.js:22)
    at Function.assertMoney (money.js:485)
    at maybeAssertValueObject (assertions.js:41)
    at maybeConvertFromValueObjectWithAssertions (extractors.js:90)
    at isShallowValidValueForField (validators.js:128)
    at assertValidValueForPreparedField (assertions.js:154)
    at create.js:199
    at lodash.js?ver=4.17.11:4911
    at baseForOwn (lodash.js?ver=4.17.11:2996)
    at lodash.js?ver=4.17.11:4880

In debugging, there IS a money object being passed through to the assertion but its failing the instanceof check. Likely because something other than Money is on the right side of the condition in the built file.

To protect against these kinds of weird compile errors, this pull:

• creates a new instanceOf( objectInstance, expectedName ) validator (in @eventespresso/validators) that can be used to verify a given object instance is an instance of the given name.
• adds unit tests for the above.

I also:

• slipped in various fixes in the entity factory entity constructor that I uncovered while testing the code snippet Brent was using.
• fixed a redundant assertion being done in the entity factory.

How has this been tested

• verified unit-tests pass.
• monkey testing in the browser console.
• Code changed impacts the EventAttendee block but it will bork immediately if there's something wrong so easily verified if it works or not.

Checklist

• I have read the documentation relating to systems affected by this pull request, see https://github.com/eventespresso/event-espresso-core/tree/master/docs
• User input is adequately validated and sanitized
• all publicly displayed strings are internationalized (usually using esc_html__(), see https://codex.wordpress.org/I18n_for_WordPress_Developers)
• My code is tested.
• My code follows the Event Espresso code style.
• My code has proper inline documentation.
• My code accounts for when the site is in Maintenance Mode (MM2 especially disallows usage of models)