Add a utility method parseAsTreeMap in NamedPathPruner

[gbhat618]

Currently converting a given tree specification into the NamedPathPruner.Tree parsing logic is present only the NamedPathPruner class and not exposed to outside. The parsed value tree and it's children are also not exposed outside (imo, it is done from an encapsulation standpoint, which is correct).

I have a use cases, I would like to parse the give tree spec, just need the list of keys. Although it would be possible

• either - write a usecase specific parsing logic based on delimiters like , [ ], but it will lead to logical mismatch between the parsing logic here and the one implemented for a specific use case.
• or - use reflection and access the children of the tree, it is not good.

To expose the parsing logic, merely changing the access specifier of methods related to parsing (parse, list, node etc.) or exposing the parsed value by getter - getTree or getChildren would break the encapsulation and may lead to problems in the downstream code.

This PR proposes to add a utility method without modifying any access specifier or changing state related logic.

I have considered alternatives such as,

• adding a new utility class such as NamedPathPrunerUtil to expose the functionality
• and, trying to extend the into child class (but needs to make the NamedPathPruner non-final)

but this proposed solution seems better one.

Testing done

• Added automated test, ensured it is running and covers 100% line coverage for the new code.

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