Add FileDescriptorId abstraction for serializable file descriptors #671

Job	Run time
rust_ci (windows-latest, stable)	3m 0s
rust_ci (windows-latest, beta)	2m 52s
rust_ci (ubuntu-latest, stable)	1m 31s
rust_ci (macos-latest, beta)	1m 47s
rust_ci (ubuntu-latest, beta)	1m 29s
rust_ci (macos-latest, stable)	1m 21s
	12m 0s

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