[NO MERGE] use a hacky way to run all the tests using new FileStream implementation

[adamsitnik]

Please ignore this PR, I just want to check if the most recent changes have not broken anything in ASP.NET before we enable them by default.

[davidfowl]

cc @sebastienros

[BrennanConroy]

FYI, I don't think this did what you wanted it to. You need to include the file in the build output otherwise it wont be included in the helix payloads and the tests wont run with this file.

You can look at https://helixre107v0xdeko0k025g8.blob.core.windows.net/dotnet-aspnetcore-refs-pull-31441-merge-aaf0039304e34f65bb/InMemory.FunctionalTests--net6.0/console.ff293fe0.log?sv=2019-07-07&se=2021-04-21T10%3A22%3A02Z&sr=c&sp=rl&sig=bLqpPJuMj8nDmM%2BvSgHzrfD%2FcbNe04iiLWPMyuWM54k%3D where we output the files in the directory of the helix payload and that file isn't included.

[BrennanConroy]

False alarm, looks like the eng folder got included, and the Directory.Build.props points to eng/.

[adamsitnik]

@BrennanConroy thank you for ensuring that it does what I was hoping it does!

[adamsitnik]

The change in runtime repo (dotnet/runtime#50166) has been merged, I am closing the PR.