Add R8_UNORM and R16_UNORM extended surface formats #768

Job	Run time
Rocky Linux MinGW	1m 8s
FreeBSD	1m 20s
iOS/tvOS SDL3 (iOS, iphoneos, arm64)	43s
Rocky Linux	1m 47s
iOS/tvOS SDL3 (iOS, iphonesimulator, x86_64;arm64)	1m 12s
Rocky Linux MinGW SDL3	56s
iOS/tvOS SDL3 (tvOS, appletvos, arm64)	47s
Debian Linux PPC	1m 43s
Debian Linux PPC SDL3	57s
iOS/tvOS SDL3 (tvOS, appletvsimulator, x86_64;arm64)	53s
Rocky Linux SDL3	1m 17s
macOS (x86_64)	46s
macOS (Universal) SDL3	1m 2s
Windows (MSVC)	1m 3s
	15m 34s

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