Add the SDL_GPU API

Project Lead: Evan Hemsley <evan@moonside.games>

Co-designer, Metal Port, Console Ports:

Co-authored-by: Caleb Cornett <caleb.cornett@outlook.com>

Production, QA, Debug:

Co-authored-by: Ethan Lee <flibitijibibo@gmail.com>

SDL_Render Driver, Bugfixes:

Co-authored-by: Andrei Alexeyev <akari@taisei-project.org>

Additional D3D12 Programming, Bugfixes:

Co-authored-by: Bart van der Werf <bluelive@gmail.com>

Bugfixes and Feedback:

Co-authored-by: Zakary Strange <zakarystrange@gmail.com>
Co-authored-by: meyraud705 <meyraud705@gmail.com>
Co-authored-by: Joshua T. Fisher <playmer@gmail.com>
Co-authored-by: Topi Ritala <ritalat@fastmail.com>
Co-authored-by: David Gow <david@ingeniumdigital.com>

Original API Proposal:

Co-authored-by: Ryan C. Gordon <icculus@icculus.org>

include/build_config/SDL_build_config_android.h

@@ -197,6 +197,8 @@
 #endif
 #endif
 
+#define SDL_GPU_VULKAN SDL_VIDEO_VULKAN
+
 /* Enable system power support */
 #define SDL_POWER_ANDROID 1