[v3] Reset error boundary when component unmounts

[alexandernanberg]

I think it would be really neat if the error boundary would automatically reset when the component unmounts. (FYI I have suspense enabled)

Let's imagine the following scenario:

1. User is on page /foo and clicks on a link to /bar
2. An error is throw in /bar and error boundary is displayed
3. User navigates back to foo
4. User clicks on the link again

IMO it doesn't make sense to display the error boundary again, but we should display the loading state again.

This would also make resetting react error boundaries easier because we could just set a new key on the component.