Implement inheritance/layering behavior for settings lists/maps

[carlos-zamora]

Description of the new feature/enhancement

TSM Inheritance (Spec #7876 + Impl #7923 ) enabled an object model representation of layering JSON. Some settings that are saved to arrays/maps (i.e. actions, color schemes) still experience a special form of layering that is not represented in the object model.

Today, the object model std::moves the list of actions/schemes down child-by-child, and directly modifies those values. We need to restructure this system to...

• track where an action/color scheme came from
• layer actions over other actions

This blocks the following work items:

• serialization for actions
• Settings UI implementation for actions
• serializing only new color schemes (ones not from defaults.json)

This also is partially related to...

• Spec for global action IDs #7175 Action IDs

[carlos-zamora]

Moved this to backlog because this is more related to #8991 and #6900. So it's not extremely urgent right now.

[carlos-zamora]

#9621 solves most of the problem here.

The remaining work to be done is for color schemes.