advancedSlicerVisual does not contain "$id" property #130
Description
"layout", "value", "background", properties have a property "$id", allowing different actionStates to have different visuals. "fillCustom" does not have the "$id" property.
"fillCustom" does seem to work with "$id" on some action states, even though it's not in the schema. For example: "$id": "selection:selected" does affect the visual when a button is selected, but "$id": "selection" has no effect.
This is confusing, and inconsistent with all other properties in both the advancedSlicerVisual and other visual definitions. It is also inconsistent with the Power BI desktop UI, which allows for manually setting fill colors for different button states.