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>

src/SDL_log.c

@@ -91,6 +91,7 @@ static const char * const SDL_category_names[] = {
     "AUDIO",
     "VIDEO",
     "RENDER",
+    "GPU",
     "INPUT",
     "TEST"
 };
@@ -270,6 +271,7 @@ static SDL_LogPriority SDL_GetDefaultLogPriority(int category)
 
     switch (category) {
     case SDL_LOG_CATEGORY_APPLICATION:
+    case SDL_LOG_CATEGORY_GPU:
         return SDL_LOG_PRIORITY_INFO;
     case SDL_LOG_CATEGORY_ASSERT:
         return SDL_LOG_PRIORITY_WARN;