move Windows code into a module #979

Job	Run time
Test CUDA support	30s
MSRV (ubuntu-latest)	24s
Test aarch64-apple-tvos	2m 31s
Clippy	15s
MSRV (windows-latest)	33s
Rustfmt	5s
Test (stable)	39s
Test (beta)	28s
Test (nightly)	27s
Test (linux32)	44s
Test (macos)	33s
Test (aarch64-ios)	39s
Test (win32)	32s
Test (win64)	34s
Test (mingw32)	33s
Test (mingw64)	34s
Test (windows-2019)	33s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	29s
	11m 3s

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