This enables HiDPI support for GTK+ on Windows, so that the
fonts and window look better on HiDPI displays. Notes for the current
work:
-The DPI awareness enabling can be disabled if and only if an application
manifest is not embedded in the app to enable DPI awareness AND a user
compatibility setting is not set to limit DPI awareness for the app, via
the envvar GDK_WIN32_DISABLE_HIDPI. The app manifest/user setting for
DPI awareness will always win against the envvar, and so the HiDPI items
will be always setup in such scenarios, unless DPI awareness is disabled.
-Both automatic detection for the scaling factor and setting the scale
factor using the GDK_SCALE envvar are supported, where the envvar takes
precedence, which will therefore disable automatic scaling when
resolution changes.
-We now default to a per-system DPI awareness model, which means that we
do not handle WM_DPICHANGED, unless one sets the
GDK_WIN32_PER_MONITOR_HIDPI envvar, where notes for it are in the
following point.
-Automatic scaling during WM_DISPLAYCHANGE is handled (DPI setting change of
current monitor) is now supported. WM_DPICHANGED is handled as well,
except that the window positioning during the change of scaling still
needs to be refined, a change in GDK itself may be required for this.
-I am unable to test the wintab items because I don't have such devices
around.
https://bugzilla.gnome.org/show_bug.cgi?id=768081
WINBOOL is MinGW-specific, so change it to BOOL, which is universally
available.
Also, Visua Studio is more picky on where __stdcall (WINAPI) is placed, so
fix that to be in-sync with what is done in the other sources.
