Have a t-ref on a DOM node with a t-key.
Change the t-key.
Before this commit, the old block removed its element from the component's refs *after*
the new block had been mounted, meaning that in effect, the resulting
ref at the end of the whole patch was null.
After this commit, we only remove an element from the component's ref if that very same
element was indeed the ref. (otherwise it means someone else has changed the ref.)
This commit makes it so that when an error occurs in an owl app and none
of the registered error handlers are able to handle it, we rethrow the
error instead of just logging it to the console and swallowing it. This
allows users of owl to handle errors that happen in owl applications by
using event listeners for error and unhandledrejection events on the
window.