DO NOT MERGE Fix bug 3121030 - Text handles erroneously appear over

extract mode IME window

Make the SelectionModifierCursorController track its show/hide state
more accurately in the presence of an extract mode IME.

Lazily initialize CursorControllers so that we don't end up creating
them for various TextViews where they are not needed.

Change-Id: Ib76a95d9e7669016cf11b8b0add8843b438068ea