Add a way to wait on process by PID #791

Job	Run time
clippy	11s
cross (ubuntu-latest)	1m 28s
cross (macos-latest)	21s
fmt	9s
msrv (ubuntu-latest)	1m 4s
security_audit	6s
msrv (windows-latest)	1m 18s
wine	1m 28s
test (ubuntu-latest, nightly)	1m 55s
test (ubuntu-latest, beta)	1m 46s
test (ubuntu-latest, stable)	1m 43s
test (windows-latest, nightly)	2m 3s
test (windows-latest, beta)	2m 7s
test (windows-latest, stable)	3m 25s
test (macos-latest, nightly)	1m 31s
test (macos-latest, beta)	1m 41s
test (macos-latest, stable)	2m 5s
test (windows-latest, nightly-x86_64-pc-windows-gnu)	2m 25s
test (windows-latest, nightly-i686-pc-windows-msvc)	2m 23s
test (windows-latest, nightly-i686-pc-windows-gnu)	2m 34s
	31m 43s

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