This follows what happens in the autotools builds.
Also fix some project namespaces and the install project where there is a typo
in a project dep, which may cause a problem during the build.
This adds the initial MSVC build items needed to build GSK under Visual Studio,
this is part of it that is required, we need to add items to the property sheets
to generate the code that is generated via glib-mkenums and glib-compile-resources.
This set includes, with the autotools scripts for the complete:
-GSK project files, which is integrated into the gtk+-4.sln.
-The NMake snippets to build the introspection files for GSK.
-The .bat files to call glib-mkenums to generate the enumeration sources.
We now need C99 features from the compiler which are only supported by
Visual Studio 2013 and later, so drop the MSVC 2008~2012 projects, and make
the baseline supported Visual Studio version be 2013. Update the build files
as a result.
