Consider possible ways to enable child process scenarios in tracing

> since `./build.sh libs.src` invokes `dotnet` internally multiple, it doesn't work. i didn't find a "follow child" option, provided by similar tools; `strace -f` or gdb (all versions) and lldb (version 14 onward) `follow-fork-mode` option.

_Originally posted by @kasperk81 in https://github.com/dotnet/msbuild/issues/7757#issuecomment-1177977054_

It's really hard to do startup tracing at runtime startup for child processes. It would be easier to have something like createdump, that allows the environment variables to have a token with a pid marker so the pipe can be distinguished per process and there can at least be a trace per process.

cc: @davmason