Add TypeScript definition for change event [⏳ 1d]

[web-padawan]

Motivation

Background: https://vaadin.slack.com/archives/D7V9RRY11/p1636969267000200

As a Lit + TypeScript user, when using Vaadin field components e.g.

<vaadin-combo-box @change=${this.fontFamilyChanged}>

... I would like get the value of the combo box without a type cast:

private fontFamilyChanged(event: Event) {
  const combo = event.target as ComboBox;
}

Proposed solution

Investigate if we could add change to ComboBoxEventMap to get this:

private fontFamilyChanged(event: ComboBoxChangeEvent) {
  const combo = event.target; // no type case needed
}

Note

Two last examples here might be useful: https://freshman.tech/snippets/typescript/fix-value-not-exist-eventtarget/