Better diagnostics when an SDL_GPU backend fails to initialize (#222) #746

Job	Run time
Rocky Linux MinGW	1m 8s
iOS/tvOS SDL3 (iOS, iphoneos, arm64)	48s
Rocky Linux	1m 49s
iOS/tvOS SDL3 (iOS, iphonesimulator, x86_64;arm64)	1m 21s
FreeBSD	1m 16s
iOS/tvOS SDL3 (tvOS, appletvos, arm64)	1m 2s
Rocky Linux MinGW SDL3	1m 12s
iOS/tvOS SDL3 (tvOS, appletvsimulator, x86_64;arm64)	59s
Debian Linux PPC	1m 50s
Debian Linux PPC SDL3	1m 8s
Rocky Linux SDL3	1m 28s
macOS (x86_64)	39s
macOS (Universal) SDL3	1m 10s
Windows (MSVC)	1m 28s
	17m 18s

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