Add Step Speed Loss (SSL) Percent and Distance

[supernovae]

Garmin HRM-600 syncing with Fenix 8, 8 Pro, or Forerunner 970 provides step speed loss data.

I'd like to see the step speed loss on my Engo eyewear in both % and distance in cm as an option.

I realize it may not be in the SDK datafield yet, but figured i'd create an issue to see if we could combine forces to get Garmin to add it to Toybox.AntPlus.RunningDynamicsData so that ActiveLook can broadcast it.

(unless y'all have other ways of grabbing this data)