Investigate improving trimability of System.Diagnostics.Process

[jkotas]

@jkotas @adamsitnik I wonder if you have some insights why Process ends up being difficult to trim?

It always drags in a lot of performance counter related functionality and the dependencies are not straightforward to break without observable behavior changes. (It may be possible to improve this, it is just not straightforward.)

For example, here is a dependency chain from https://github.com/MichalStrehovsky/sizoscope for a simple app that just does Process.Start("notepad.exe").WaitForExit()

Originally posted by @jkotas in #126192 (comment)

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[tmds]

On Linux, these seem to be adding size:

• ToString brings with it everything needed for ProcessInfo (though it only needs the ProcessName):

runtime/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.cs

Lines 1487 to 1514 in 2f94e9d

	public override string ToString()
	{
	string result = base.ToString();
	try
	{
	if (Associated)
	{
	_processInfo ??= ProcessManager.GetProcessInfo(_processId, _machineName);
	if (_processInfo is not null)
	{
	string processName = _processInfo.ProcessName;
	if (processName.Length != 0)
	{
	result = $"{result} ({processName})";
	}
	}
	}
	}
	catch
	{
	// Common contract for ToString methods is never throw.
	// Handle cases where a process would terminates immediately after our checks
	// and/or cause ProcessManager to throw an exception.
	}
	return result;
	}

• Support for redirected I/O brings in Sockets which then brings in SocketsTelemetry (ActivitySource, ...).

[tmds]

@jkotas @adamsitnik if you have some suggestions based on the above, I'd be interested to try them out.

[adamsitnik]

• Support for redirected I/O brings in Sockets which then brings in SocketsTelemetry (ActivitySource, ...).

I think once we have #47631 which should allow to poll any descriptor using epoll/kqueue we can improve #125512 and make FileStream use it (currently the async read/write methods are going to perform a blocking poll). Then FileStream would be great for any file on every OS and we could just use FileStream for every platform.