Design MLIR interfaces for selected clang AST nodes. #643

Prerequisites

• I have read the documentation and the proposed feature is not implemented.

Description

To support clang static analyzer, we need to provide some APIs of the AST nodes. Proposed solution is to implement MLIR interface that expose methods needed by the static analyzer passes (and necessary utilities).

For each interface, the supported methods do not need to be exhaustive - we only want to lazily add things that are needed by the passes we care about.