Implement BlockState utility functions (IsDescendantOf, LowestCommonAncestor, Range)

[timwu20]

Issue Summary

From design doc:

The utilization of already introduced utility functions and types can be used to implement the following BlockState methods.

IsDescendantOf(parent, child common.Hash) (bool, error)
LowestCommonAncestor(a, b common.Hash) (common.Hash, error)
Range(startHash, endHash common.Hash) (hashes []common.Hash, err error)
RangeInMemory(start, end common.Hash) ([]common.Hash, error)

IsDescendantOf can be found in client/api/utils (see code).

LowestCommonAncestor can be found in primitives/blockchain (see code)

Range and RangeInMemory can be implemented by using blockchain.TreeRoute. The constructor NewTreeRoute takes a start and end block hash. We should also remove the usage of RangeInMemory given that all finalized and non-finalized blocks are now in the same db.Backend. So a small refactor to the only external usage in dot/core should be updated to use Range.

These functions should be added to the translation shim since they are used externally from dot/state.

Acceptance Criteria

• Implementation of utility functions.
• Unit tests.