Vulkan: Backport frames-in-flight logic from SDL_GPU #736

Job	Run time
Rocky Linux MinGW	1m 14s
FreeBSD	1m 14s
iOS/tvOS SDL3 (iOS, iphoneos, arm64)	46s
iOS/tvOS SDL3 (iOS, iphonesimulator, x86_64;arm64)	1m 1s
Rocky Linux	1m 47s
iOS/tvOS SDL3 (tvOS, appletvos, arm64)	53s
Rocky Linux MinGW SDL3	1m 8s
Debian Linux PPC	1m 52s
iOS/tvOS SDL3 (tvOS, appletvsimulator, x86_64;arm64)	1m 2s
Debian Linux PPC SDL3	1m 0s
Rocky Linux SDL3	1m 30s
macOS (x86_64)	25s
macOS (Universal) SDL3	1m 14s
Windows (MSVC)	1m 6s
	16m 12s

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