Throw error when passing non "JSON parsable" strings to props

When passing a string with an array I would expect the console to throw an error in case my prop is not parsable as JSON.

Currently, it fails silently.

Example:
```html

```

In this example I would expect an error in the console containing a message like:
`Couldn't parse "my-attribute" as JSON. Make sure you're using valid JSON syntax on this attribute's value.`

No source file or test is named in the issue. Start by locating the prop/attribute parsing entry point in the TypeScript web-component code and reproduce the HTML example; done means invalid JSON produces the requested console error while valid values continue to work.

Written by the indexing model from the issue text.