Fix line slop issue at end of line for Thai & CJK

Previously touch slop for line movement was based on the line position
of the HandleView, not the previous line touched.

Thai and CJK languages don't have a space at the end of a line so
the handle jumps to the beginning of the next line. This meant that
when calculating the touch slop it'd be from the incorrect line.

This CL tracks the previous line touched and uses that instead to
calculate touch slop and applies it to the selection and insertion
handles.

Note this is *not* added to the drag accelerator because
it does not have the problem of the handle jumping to the next line
since it has no handles.

Bug: 21925162
Change-Id: If4b231725c06489ec780a5b5a308ceffee804c20