Re-work the Dart Devtools integration after Dart VM work

[jwren]

PR after chatting with @jacob314

After @bkonyi is done with his current changes to how DevTools will work with Dart processes, the DevTools action in the Flutter Plugin should be updated to continue to work with DevTools.

@bkonyi please update this issue when the change has landed in the Dart VM.

After this work is done please ping me (@jwren) to ensure that we get appropriate changes pushed into the Dart Plugin for IJ.

[bkonyi]

This has landed in the standalone SDK but there's no work to be done for Flutter applications at this point. There's currently no way to disable DevTools for the standalone VM, but there's a CL in the works adding a new --no-enable-devtools. Is there any particular flow that you're concerned about?

[jacob314]

@bkonyi we don't plan to disable DevTools for the standalone VM. We want to use the version of DevTools you embed with the VM to simplify the install process and eliminate the pub global activate step.
Fyi @helin24.