win32: Require Windows 10

All versions older than Windows 10 are out of support and no longer
receive updates, so we do not want to support them.

We also want to move towards APIs that requires Windows 10 - like
Direct3D 12 - and not having them optional simplifies our code.

See the discussion in !7895 for more details.

meson.build

@@ -64,7 +64,7 @@ if host_machine.system() == 'windows'
   add_project_arguments(['-DUNICODE',
                          '-D_UNICODE',
                          '-DCOBJMACROS',
-                         '-D_WIN32_WINNT=_WIN32_WINNT_WIN7'], language: 'c')
+                         '-D_WIN32_WINNT=_WIN32_WINNT_WIN10'], language: 'c')
 endif
 
 # Use debug/optimization flags to determine whether to enable debug or disable