Vulkan: Include Win32 extensions definitions

Includes win32 specific extensions definitions when including
`vk_common.hh`. Inside `gpu_context.cc` vulkan needs to be
included before opengl, otherwise windows 10 builders will
report a warning.

```
[6421/7520] Building CXX object source\blender\gpu\CMakeFiles\bf_gpu.dir\intern\gpu_context.cc.obj
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared\minwindef.h(130): warning C4005: 'APIENTRY': macro redefinition
C:\Users\blender\git\blender-vexp\blender.git\lib\windows_x64\epoxy\include\epoxy/gl.h(59): note: see previous definition of 'APIENTRY'
```

Pull Request: https://projects.blender.org/blender/blender/pulls/137134

intern/ghost/GHOST_Types.h

@@ -14,7 +14,7 @@
 #  ifdef __APPLE__
 #    include <MoltenVK/vk_mvk_moltenvk.h>
 #  else
-#    include <vulkan/vulkan.h>
+#    include <vulkan/vulkan_core.h>
 #  endif
 #endif
 

source/blender/gpu/intern/gpu_context.cc

@@ -33,13 +33,13 @@
 #include "gpu_private.hh"
 #include "gpu_shader_private.hh"
 
+#ifdef WITH_VULKAN_BACKEND
+#  include "vk_backend.hh"
+#endif
 #ifdef WITH_OPENGL_BACKEND
 #  include "gl_backend.hh"
 #  include "gl_context.hh"
 #endif
-#ifdef WITH_VULKAN_BACKEND
-#  include "vk_backend.hh"
-#endif
 #ifdef WITH_METAL_BACKEND
 #  include "mtl_backend.hh"
 #endif

source/blender/gpu/vulkan/vk_common.hh

@@ -10,10 +10,17 @@
 
 #include <typeinfo>
 
+#ifdef _WIN32
+#  include "BLI_winstuff.h"
+#endif
+
 #ifdef __APPLE__
 #  include <MoltenVK/vk_mvk_moltenvk.h>
 #else
 #  include <vulkan/vulkan.h>
+#  ifdef _WIN32
+#    include <vulkan/vulkan_win32.h>
+#  endif
 #endif
 
 #include "vk_mem_alloc.h"