Add FileDescriptorId abstraction for serializable file descriptors #668

Job	Run time
rust_ci (ubuntu-latest, stable)	17s
rust_ci (windows-latest, stable)	14s
rust_ci (macos-latest, beta)	17s
rust_ci (macos-latest, stable)	13s
rust_ci (ubuntu-latest, beta)	20s
rust_ci (windows-latest, beta)	15s
	1m 36s

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