The problem was that when the editor had no events the cursor was not
blinking because the event loop was blocking on wait_event.
Now we no longer calls wait_event without a timeout if the windows has
the focus. When the window has the focus the timeout is set to 1 / fps
so that the cursor can blinks.
In addition we react to the "focus lost" event to ensure the documents
are redrawn without the cursor.
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