[Feat][C++] Improve high-level APIs of the C++ library to provide the view and operations at the graph level

**Is your feature request related to a problem? Please describe.**
Currently, the C++ library of GraphAr provides some high-level structures and related methods, i.e., `VerticesCollection` and `EdgesCollection`. However, a view of the whole graph and the operations are required for conduct processing more conveniently.

**Describe the solution you'd like**
Proposal TBF

No files or tests are named. Start by reviewing the existing C++ VerticesCollection and EdgesCollection structures and methods, then clarify the proposed whole-graph view and operations; the issue currently has no defined completion criteria because its solution is marked TBF.

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