[checkbox] Regression: the checkbox is not clickable over the whole area

[vursen]

Description

Since we've changed the checkbox such that it relies on the native input change event rather than the click event on the component (#2539), now it can be switched only by click on the label or input while before it was clickable over the whole area.

Expected outcome

The whole area is clickable.

Actual outcome

Click on the corners does not trigger change.

Live Demo (optional)

Screen.Recording.2021-09-30.at.16.45.44.mov

Minimal reproducible example

<vaadin-checkbox value="economy">Economy</vaadin-checkbox>

Steps to reproduce

1. Run yarn debug --group checkbox.
2. Open https://localhost:8000/dev/checkbox.html