[ProcessLauncher] Explicitly set diagnostic port configs

[mdh1418]

Partly addresses #5501

Child processes started by diagnostic tooling set a DOTNET_DiagnosticPort environment variable, specifying only the path.
The runtime defaults to a connect type port in suspend mode, which isn't clear from the end user's viewpoint, as logging will only reveal the DiagnosticPort value. Instead, we can mitigate confusion by explicitly setting the config from the tooling side.

Before

The runtime has been configured to pause during startup and is awaiting a Diagnostics IPC ResumeStartup command from a Diagnostic Port.
DOTNET_DiagnosticPorts="dotnet-trace-48696-20250614_161420.socket"
DOTNET_DefaultDiagnosticPortSuspend=0

Now

The runtime has been configured to pause during startup and is awaiting a Diagnostics IPC ResumeStartup command from a Diagnostic Port.
DOTNET_DiagnosticPorts="dotnet-trace-29004-20250616_134924.socket,suspend,connect"
DOTNET_DefaultDiagnosticPortSuspend=0

[hoyosjs]

This will not really solve the issue for the customer sadly - this is something that needs a little more work in trace to at least give better warnings to the tool. I'm ok with letting this go in - but we need to warn about child processes/document this.

[noahfalk]

The change looks fine, but we should call out that this is just one element of fixing the overall problem. We should not mark the issue fixed based on this PR alone.

[lateralusX]

The underlying problem is that the child processes inherit env variables by default, so if env variables are not going to be inherited by a child processes spawned by the process that got spawned by dotnet-trace (and have its DOTNET_DiagnosticPorts set), it needs to be cleared, but only for the env used when spawning the child process. The code spawning the child process needs to make sure this env is not inherited in its call to Process.Start.

[mdh1418]

Thanks everyone for all the clarifying comments, modified to not close the tracking issue. Will follow Noah's outline and have this change just clarify that the env vars will suspend the runtime in the child process.