BUG #15882: Fixes performance of hover-points mode.
Hover-points-tooltips mode was slower than interactively selecting points. The reason was that while we reused selection buffers for latter, the former was re-rendering the selection buffers on each mouse move. This was because the cache preserving mechanisms that the render view has for preserving selection color buffers while interacting in an interactive selection mode were not being employed for hover-points mode. Fixed that by chaning the render view's interaction mode state so as far as the render view goes, it's in the same mode as the interactive point/cell selection and will use the same caching techniques.