Introduce wgpu::Surface and implement it for HWND, X11 and Metal

This is another step to implement webgpu.h swapchains, Surface is
essentially a union type of all the types of windows that can be used to
create swapchains.

Changes to allow implementing wgpu::Surface and test its creation are:

 - Add GLFWUtils.cpp/.h/_metal.mm  that contains helpers used to use
WebGPU with GLFW. This deprecates BackendBinding.h that will be removed
when the NXT swapchain is removed.
 - Add a `dawn_use_x11` GN variable to factor all the places in BUILD.gn
where we checked whether we should use X11.
 - Add a `supports_glfw_for_windowing` GN variable in the main BUILD.gn
file to control which configuration tests and samples using GLFW can be
built.
 - Add a ObjCUtils.h to contain some ObjC functionality that we'd need
in files that otherwise would be C++ (so that they can be compiled on
all platforms).

Bug: dawn:269

Change-Id: I25548142a1d1d1f05b0f4d71aa3bdc4698d19622
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/15081
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>

src/common/BUILD.gn

@@ -75,7 +75,7 @@ config("dawn_internal") {
     defines += [ "DAWN_ENABLE_BACKEND_VULKAN" ]
   }
 
-  if (is_linux && !is_chromeos) {
+  if (dawn_use_x11) {
     defines += [ "DAWN_USE_X11" ]
   }
 

src/common/windows_with_undefs.h

@@ -26,6 +26,7 @@
 #include <windows.h>
 
 // Macros defined for ANSI / Unicode support
+#undef CreateWindow
 #undef GetMessage
 
 // Macros defined to produce compiler intrinsics

src/common/xlib_with_undefs.h

@@ -30,4 +30,6 @@
 #undef None
 #undef Always
 
+using XErrorHandler = int (*)(Display*, XErrorEvent*);
+
 #endif  // COMMON_XLIB_WITH_UNDEFS_H_