fix(event-construction): use CustomEvent constructor

[w0wka91]

• Closes Cannot read property 'indexOf' of undefined when using .type() #6125

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[w0wka91]

It looks like the constructor that was used before to create custom events(e.g. KeyboardEvent) is not supported/available in all browsers:
event = new win['Event'](eventType, eventOptions)
So I replaced this with the CustomEvent constructor which is supported by all major browsers except IE.

[jennifer-shehane]

I've manually confirmed that this does solve the original issue.

We will need a test to cover this change. A test that fails without this change and now passes with this change. Can you add this?

Keyboard tests can be found here: https://github.com/cypress-io/cypress/blob/develop/packages/driver/test/cypress/integration/e2e/keyboard_spec.coffee#L4:L4

To run the tests:

• within cypress root, run npm i
• cd to cypress/packages/runner and run npm watch
• cd to cypress/packages/driver and run cypress open
• click on the test you're writing to run it within Cypress

Instructions for running the driver tests can always be found here: https://github.com/cypress-io/cypress/blob/develop/packages/driver/README.md

[kuceb]

I don't see why we can't use the Event constructor. and notice the win is the AUT iframe Window, which is the correct context, whereas CustomEvent here is the spec iframe. I think #6125 needs a different fix, since this worked in 3.4.1 while using the Event constructor. Closing this for now