feat: add Observer Map to FAST HTML

[janechu]

🙋 Feature Request

Since the declarative markup in FAST HTML uses simple dot notation for paths, we should be able to create an Observer Map to automatically observe objects, arrays, and keys.

🤔 Expected Behavior

Observation happens automatically.

😯 Current Behavior

We have to manually observe all complex objects which is quite a hassle.

💁 Possible Solution

Create a map of all binding data locations and observe them, utilize this as part of the TemplateElement as this will have access to the paths in the declarative logic.

Additionally this should export the path utility in case it is useful for other applications such as a state service that must access some data.