SDL: Add support for FNA3D_BACKBUFFER_SCALE_NEAREST #835

Job	Run time
FreeBSD (SDL2)	1m 4s
Fedora Linux MinGW (SDL2)	54s
Steam Linux Runtime (SDL2)	1m 14s
iOS/tvOS (SDL3) (iOS, iphoneos, arm64)	55s
Fedora Linux MinGW (SDL3)	48s
iOS/tvOS (SDL3) (iOS, iphonesimulator, x86_64;arm64)	1m 14s
Debian Linux PPC (SDL2)	1m 42s
Debian Linux PPC (SDL3)	56s
iOS/tvOS (SDL3) (tvOS, appletvos, arm64)	47s
iOS/tvOS (SDL3) (tvOS, appletvsimulator, x86_64;arm64)	54s
Steam Linux Runtime (SDL3)	1m 15s
macOS (x86_64) (SDL2)	31s
macOS (Universal) (SDL3)	57s
Windows MSVC (SDL2)	1m 9s
Windows MSVC (SDL3)	1m 26s
	15m 46s

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