feat: export our own async version of fireEvent

[mlrawlings]

Description

The promise returned from fireEvent resolves once any pending updates caused by the event have completed (currently uses wait() to accomplish this).

BREAKING CHANGE: fireEvent no longer returns a boolean and instead returns a promise.

Motivation and Context

Since DOM updates are async in Marko, all assertions following an event needed to wait for a DOM change themselves.

fireEvent.click(someNode);
wait(() => expect(someNode).to.have.attr("newAttr"));

Now, you can wait for the effect of a fireEvent method:

await fireEvent.click(someNode);
expect(someNode).to.have.attr("newAttr");

Checklist:

• I have updated/added documentation affected by my changes.
• I have added tests to cover my changes.