Adds mixdown generation #697

Job	Run time
Build macOS (arm64)	21m 39s
Build macOS (x86_64)	9m 54s
Ubuntu 20.04 AppImage (x86_64)	19m 47s
Windows MSVC 2019 (x86)	20m 49s
Ubuntu 20.04 AppImage (x86_64, gcc 11)	7m 34s
Windows MSVC 2019 (x86_64)	20m 12s
Ubuntu 22.04 AppImage (x86_64)	7m 21s
Source Tarball	6m 40s
Windows MSVC 2022 (x86)	26m 4s
Windows MSVC 2022 (x86_64)	24m 35s
Package macOS (x86_64, arm64, universal)	0s
	2h 44m 35s

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