Quicktags: move focusing the editor after inserting content to the end of the code blocks. Fixes a bug in Chrome where both the textarea and the window may auto-scroll to unexpected position on clicking a Quicktags button. Part props avryl, fixes #29944 for trunk.

git-svn-id: https://develop.svn.wordpress.org/trunk@29884 602fd350-edb4-49c9-b593-d223f7449a82