Make diagnostics tools aware of MacOS sandboxed apps

[josalem]

Currently, the diagnostics apps only are aware of pipes that exist in $TMPDIR or /tmp on Mac and therefore could not trace a program running inside a sandbox (AppGroupContainer).

This will most likely need to be an optional flag that specifies an AppGroupId in order for the tool to know where to look for the pipe. This could be generalized to look in a path prefix, or a specific AppGroupId's container dir.

Oden, this new IPC protocol doesn't affect the debugger transport channel or all the work you did to support MacOS containers. This is a new channel allowing some of new tools like trace events, profiler attach and dump generation to communicate with the runtime. We just want to make sure it also runs in a MacOS container.

Got it. Yeah, if we take the sandbox scenario into consideration while designing this - it would be great. I am sure as time passes, .net core will be used in more apps and sandboxing is a requirement for releasing to Apple store. Esp. with .Net 5 plans to allow xamarin with .net core runtime to work side by side.

Originally posted by @odhanson in https://github.com/dotnet/diagnostics/pull/198