This is the first basic functionality to get the active
EditView with EditEngine work in the Overlay which all
Apps support. Reason is that the current EditEngine 'plugs'
into the Window and uses Invalidate() calls to repaint
deeply everything under a text change. While this is
acceptable for simple cases it can get very slow when
there are excessive, expensive to paint objects in the
background, e.g. MasterPages in Draw/Impress with gradients
and other stuff. This was avoided in older versions (LO51)
by 'guessing' a good BackgrundColor by the EditEngine,
not invalidating but painting actively using that guess
(with better or worse results) which someone removed.
For the future it is anyways the better way to get the
EditEngine functionality to Overlay and using Primitives,
this will be a first step. This may enable Text Editing
without repainting the Background (fast), using a non-XOR
selection paint and more. It will need thorough testing
and further experimenting due to EditEngine being used in
many places (DrawObjects, Calc Cells, Formular Fields,
Controls, ...)

Change-Id: Ib9eb0f3999fd61a82ddf7a60ab1ea6ccda3a60da