bug: ion-checkbox is toggled by ion-item click

# Bug Report

**Ionic version:**

[x] **4.x**

**Current behavior:**

If you have the following markup, any click or tap on the ion-item will toggle the ion-checkbox:

```

```

**Expected behavior:**

The ion-checkbox should only toggle when it is clicked, or the click event from the ion-item should be cancellable.

**Steps to reproduce:**

**Related code:**

[Codepen](https://codepen.io/bsbechtel/pen/YzXWKOW?editors=1100)

**Other information:**

This issue has been brought up multiple times and not fixed: [19590](https://github.com/ionic-team/ionic/issues/19590) [15850](https://github.com/ionic-team/ionic/issues/15850) [17832](https://github.com/ionic-team/ionic/issues/17832)

**Ionic info:**

```
insert the output from ionic info here
```

Start with the CodePen reproduction and inspect the interaction between ion-item and ion-checkbox using the markup in the report. Trace how clicks propagate between these components and check existing related issues 19590, 15850, and 17832. Done means clicking the item no longer toggles the checkbox, or the item click can be cancelled.

Written by the indexing model from the issue text.