windows: add CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT, and CTRL_SHUTDOWN_EVENT

[tianon]

This is part of the changes necessary to allow simulated SIGTERM on Windows (these are the relevant events for SetConsoleCtrlHandler that would correspond to SIGTERM on Unix).

See https://docs.microsoft.com/en-us/windows/console/handlerroutine for a good documentation source upstream to confirm these values.

Updates golang/go#7479

(This exists under src/cmd/vendor/golang.org/x/sys/windows/types_windows.go in https://github.com/golang/go, so I figured I would start here and follow up with a https://github.com/golang/go PR/CL if reviewers here were amenable to this half.)

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Patch Set 1: Run-TryBot+1 Code-Review+2

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This PR is being closed because golang.org/cl/187578 has been merged.