Fix VTU don't return key property to event when use trigger.('eventName.key')

[voskresla]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Other, please describe: fix test convert a registered key name to a key code in test/specs/wrapper/trigger.spec.js

Does this PR introduce a breaking change? (check one)

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the dev branch.
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue-test-utils/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

Other information:
If in our code exist check like this:

import { Key } from 'w3c-keys'
...
handleOnKeyDown(e: KeyboardEvent) {
	const tab = e.key === Key.Tab
	const escape = e.key === Key.Escape

	if (tab || escape) {
		...doSmth
	}
}

we can't test it by fire event like this

await input.trigger('keydown.tab')

Because VTU don't return key property in event when triggered by eventName.keyName.

Of course we can test it like this )

await input.trigger('keydown', {
	key: 'Tab',
})

[lmiller1990]

Thanks, sorry it took so long to review! I will do a release this week probably.