Introduce DPI scale factor for Hi-DPI displays.

This is supposed to stay 1 (no scale) for printers and default virtual
devices, but should be set accordingly (2 or 3) for windows and virtual
devices derived from windows.

Various VCL widgets or paint operations should incrementally become aware of
this, and changed so that they draw nicely on the Hi-DPI displays.  This patch
only introduces the behavior for waved lines.

The default is currently being set depending on the DPI setting only; could be
changed to a more clever way if necessary.

Change-Id: I71118f9ab6b64028d1eeee76e860e999d5cd9d19
Reviewed-on: https://gerrit.libreoffice.org/8516
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>