Our current caret cleanup code has two problems. One of them is that we don't clean up the caret correctly on dragexit (the same way that we do on drop), and the second problem is that we cache the created caret, which is unnecessary, and could probably cause us to use a stale caret object if the presshell dies, for example. I have a patch which fixes both of these issues.

Let's clean this up even more. The caret itself tracks its drawn status, so maintaining it in nsEditorEventListener is both error prone and useless, so let's get rid of mCaretDrawn altogether.