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....

src/dynapi/SDL_dynapi.exports

@@ -1290,3 +1290,4 @@ _SDL_LoadJPG
 _SDL_HasSVE2
 _SDL_GamepadHasCapSense
 _SDL_GetGamepadCapSense
+_SDL_WGPU_CreateSurface

src/dynapi/SDL_dynapi.sym

@@ -1291,6 +1291,7 @@ SDL3_0.0.0 {
     SDL_HasSVE2;
     SDL_GamepadHasCapSense;
     SDL_GetGamepadCapSense;
+    SDL_WGPU_CreateSurface;
     # extra symbols go here (don't modify this line)
   local: *;
 };

src/dynapi/SDL_dynapi_overrides.h

@@ -1317,3 +1317,4 @@
 #define SDL_HasSVE2 SDL_HasSVE2_REAL
 #define SDL_GamepadHasCapSense SDL_GamepadHasCapSense_REAL
 #define SDL_GetGamepadCapSense SDL_GetGamepadCapSense_REAL
+#define SDL_WGPU_CreateSurface SDL_WGPU_CreateSurface_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -1325,3 +1325,4 @@ SDL_DYNAPI_PROC(SDL_Surface*,SDL_LoadJPG,(const char *a),(a),return)
 SDL_DYNAPI_PROC(bool,SDL_HasSVE2,(void),(),return)
 SDL_DYNAPI_PROC(bool,SDL_GamepadHasCapSense,(SDL_Gamepad *a,SDL_GamepadCapSenseType b),(a,b),return)
 SDL_DYNAPI_PROC(bool,SDL_GetGamepadCapSense,(SDL_Gamepad *a,SDL_GamepadCapSenseType b),(a,b),return)
+SDL_DYNAPI_PROC(WGPUSurface,SDL_WGPU_CreateSurface,(SDL_Window *a,WGPUInstance b),(a,b),return)