Add `SystemStart` and `BootStart` start types #71

Job	Run time
test (i686-pc-windows-gnu, stable)	2m 59s
test (x86_64-pc-windows-gnu, stable)	3m 53s
test (i686-pc-windows-msvc, stable)	33s
test (x86_64-pc-windows-msvc, stable)	38s
test (x86_64-pc-windows-msvc, beta)	31s
test (x86_64-pc-windows-msvc, nightly)	41s
test (x86_64-pc-windows-msvc, 1.58.0)	1m 55s
	11m 10s

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