patch 9.0.1970: win32: high-dpi support can be improved

patch 9.0.1970: win32: high-dpi support can be improved

Problem:  win32: high-dpi support can be improved
Solution: implement WM_GETDPISCALEDSIZE

win32: Better support of Per-Monitor V2 High DPI

Implement WM_GETDPISCALEDSIZE.
It is not so easy to calculate the new size without actually changing
the size. So, this returns an approximate size.

This doesn't work well when a bitmap font (e.g. FixedSys) is selected,
but I think this is acceptable.

closes: #11812
closes: #13252

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ken Takata <kentkt@csc.jp>