Make ProcessInfo / DiagnosticClient.GetProcessInfo public

[xoofx]

In the same principle than #5086, I'm trying to chase down internal APIs that require to be accessed via System.Reflection or that are used also outside of this repository by other .NET tooling.

I would like to make ProcessInfo and DiagnosticClient.GetProcessInfo public. It seems that the API has been fairly stable in the past years with what looks like mostly additions to the API. This API is particularly interesting to surface target process information (runtime version, RID...etc.)

I can make a PR if this proposal is accepted.

[noahfalk]

@xoofx - sorry this went unattended for a long while! Making that API seems like a fine thing to do.

cc @dotnet/dotnet-diag