Support Per-metric Multiple Device Selection and Targetless Graphing

[planetchili]

API now fully implemented and the concept of the "active adapter" is retired. It is now possible to have an overlay where telemetry from multiple adapters is shown simultaneously. UI needs to be upgraded to surface this capability.

Also, it is possible to graph telemetry without any presenting target. In this case the independent widget window would be forced. UI and backend needs to be upgraded to allow this use case. Will enable certain scenarios such as monitoring CPU/GPU during ML/AI training or inference operations, where typically there is no presenter to target.