Create an AST framework with ability to traverse, join, exclude and find subtrees.

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Currently all patterns are evaluated on a single file. We need a tool to construct arbitrary AST by filtering and merging together different subtrees of parsed file and use it for pattern evaluation.
More precisely, we need to be able to extract classes from a package and methods and fields from a class. Analyze dependencies of methods (it could be class fields and other methods). Split the dependency graph by connected components. And create an AST with the only methods and fields from the component.