Enable Add-Content to share read access to other tools while writing content

[SteveL-MSFT]

PR Summary

Add-Content uses a writer that currently sets share access to write. So if using a tool like tail to read a log file while trying to write to it will fail. Fix is to change share access to readwrite which will allow other processes to continue to read from it while the writer writes new content.

Fix #5924

PR Checklist

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• Summarized changes
• Change is not breaking
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• User-facing changes
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  • User-facing Documentation needed
    • Issue filed - Issue link:
• Testing - New and feature
  • Not Applicable or can only be tested interactively
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  • Make sure you've added a new test if existing tests do not effectively test the code changed
    • Add [feature] if the change is significant or affects feature tests

[iSazonov]

We always have problems with async tests. Do we really need the test? I'd only add an comment in C# code.

[SteveL-MSFT]

I kind of agree on async tests being inherently fragile. Perhaps for this one a comment in the code is sufficient.

[anmenaga]

Can make it sync:

1. open a file with FileStream(FileAccess.Read, FileShare.ReadWrite) and keep it open.
2. run new Add-Content (with FileAccess.Write, FileShare.ReadWrite)
3. close FileStream from 1). The test should not throw.

The old Add-Content (with FileShare.Write) in 2) would throw.

[SteveL-MSFT]

Good suggestion, let me see if that repros the original issue.

[adityapatwardhan]

Please see if these changes are possible. It would harden the test.

[SteveL-MSFT]

@anmenaga that worked perfectly and so simple :)

[adityapatwardhan]

Use ForEach-Object instead of %

[voytas75]

is (1..10).foreach{...} faster then ForEach-Object?