Began work on WGPU video backend

Currently only supports Wayland, and it's quite..... bad

This is a DRAFT! Just a small proof-of-concept.

I'll submit a draft PR to the SDL project to see if I should continue
development.

If this is greenlit, I might making consider a WGPU SDL_GPU backend if
wgpu-native is in a good enough state (maybe Dawn if it isn't?)

No promises though! Don't get angry at me if I don't!

Current known issues:
1: Error handling is sparse.
2: It only supports the shared library version of wgpu-native, and it
does that by just loading it whenever it needs to do something
3: wgpu-native is bad and doesn't implement wgpuGetProcAddress so we're
just using SDL_LoadFunction instead. I'd much prefer using the native
wgpuGetProcAddress but alas....

include/SDL3/SDL.h

@@ -85,6 +85,7 @@
 #include <SDL3/SDL_tray.h>
 #include <SDL3/SDL_touch.h>
 #include <SDL3/SDL_version.h>
+#include <SDL3/SDL_wgpu.h>
 #include <SDL3/SDL_video.h>
 #include <SDL3/SDL_oldnames.h>
 

include/SDL3/SDL_wgpu.h

@@ -0,0 +1,42 @@
+/**
+ * # CategoryWGPU
+ *
+ * Experimental support for the wgpu-native C bindings.
+ */
+
+#ifndef SDL_wgpu_h_
+#define SDL_wgpu_h_
+
+#include <SDL3/SDL_video.h>
+
+#include <SDL3/SDL_begin_code.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef WEBGPU_H_
+#define WGPU_OBJECT_ATTRIBUTE(object) typedef struct object##Impl *object;
+#endif
+
+WGPU_OBJECT_ATTRIBUTE(WGPUSurface)
+WGPU_OBJECT_ATTRIBUTE(WGPUInstance)
+
+#undef WGPU_OBJECT_ATTRIBUTE
+
+/**
+ * Create a new WGPU surface.
+ *
+ * \param window The window which the surface will attach itself to.
+ * \param instance The WGPU instance.
+ *
+ * \returns A WGPUSurface. Can be NULL if there was a failure.
+ */
+extern SDL_DECLSPEC WGPUSurface SDLCALL SDL_WGPU_CreateSurface(SDL_Window *window, WGPUInstance instance);
+
+#ifdef __cplusplus
+}
+#endif
+#include <SDL3/SDL_close_code.h>
+
+#endif // SDL_wgpu_h_

include/build_config/SDL_build_config.h.cmake

@@ -487,6 +487,9 @@
 /* Enable Metal support */
 #cmakedefine SDL_VIDEO_METAL 1
 
+/* Enable experimental WGPU support */
+#cmakedefine SDL_VIDEO_WGPU 1
+
 /* Enable GPU support */
 #cmakedefine SDL_GPU_D3D11 1
 #cmakedefine SDL_GPU_D3D12 1