Add a function to Relisten on a pipe

[notnoop]

This adds a method for re-listening on an existing pipe. Helpful in case where the pipe creator process is restarted and the pipe still exists. winio.ListenPipe fails now if the pipe exists already.

[msftclas]

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[endocrimes]

@notnoop In case it breaks CLA stuff, feel free to ping me and I can open a new PR

[endocrimes]

@kevpar if I re-open this PR is it likely to be reviewed+accepted? - I'd like to drop my fork (partially to remove myself from the Nomad build process) - and so they can use newer versions of the library.