Move `input.cpp` to a new directory #648

Job	Run time
Linux (arm64) / build (Debug)	2m 47s
Linux (x86_64) / build (Debug)	4m 23s
Linux (arm64) / build (Release)	7m 53s
Android / build (Debug)	1m 5s
Linux (x86_64) / build (Release)	3m 59s
iOS / build (Debug)	4m 5s
Linux (arm64) / build (RelWithDebInfo)	3m 3s
Android / build (Release)	1m 24s
Linux (x86_64) / build (RelWithDebInfo)	4m 0s
iOS / build (Release)	3m 54s
Android / build (RelWithDebInfo)	1m 1s
iOS / build (RelWithDebInfo)	3m 19s
macOS (arm64) / build (Debug)	7m 12s
macOS (x86_64) / build (Debug)	9m 15s
macOS (arm64) / build (Release)	11m 12s
tvOS / build (Debug)	6m 29s
macOS (x86_64) / build (Release)	9m 48s
Windows (x86_64) / build (Debug)	10m 50s
macOS (arm64) / build (RelWithDebInfo)	9m 41s
tvOS / build (Release)	3m 44s
macOS (x86_64) / build (RelWithDebInfo)	8m 57s
Windows (x86_64) / build (Release)	9m 24s
tvOS / build (RelWithDebInfo)	6m 58s
Windows (x86_64) / build (RelWithDebInfo)	10m 56s
	2h 25m 19s

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