This commit also changes input handling to be more like it was in the
previous editor. We're using textInput rather than input events because
they are emitted *before* characters are inserted, enabling much simpler
detection of characters inserted via the accented-character menu on
OS X.
Previously I avoided this because something about it was causing reflows
in the old editor, but in this editor that doesn't seem to be a problem,
and it's actually faster.
1c410cbf5a