Move windows.h to before check for minimum version instead of after

This tests the value of _WIN32_WINNT before including windows.h. This is the wrong thing to do. If you want to require a minimum version you firts include windows,h and then check _WIN32_WINNT.

As described in this issue: https://github.com/microsoft/vcpkg/issues/7281

include/grpc/impl/codegen/port_platform.h

@@ -46,6 +46,8 @@
 #define NOMINMAX
 #endif /* NOMINMAX */
 
+#include <windows.h>
+
 #ifndef _WIN32_WINNT
 #error \
     "Please compile grpc with _WIN32_WINNT of at least 0x600 (aka Windows Vista)"
@@ -56,8 +58,6 @@
 #endif /* _WIN32_WINNT < 0x0600 */
 #endif /* defined(_WIN32_WINNT) */
 
-#include <windows.h>
-
 #ifdef GRPC_WIN32_LEAN_AND_MEAN_WAS_NOT_DEFINED
 #undef GRPC_WIN32_LEAN_AND_MEAN_WAS_NOT_DEFINED
 #undef WIN32_LEAN_AND_MEAN