[clang] [clang][dataflow] Expose fields, globals, and functions referenced. (PR #88534)

[via cfe-commits]

martinboehme wrote:

DataflowAnalysisContext.h is starting to accumulate more and more functions that serve to extract various types of information from the AST; these aren't really related to the `DataflowAnalysisContext`, so I wonder if it's time to separate these out into their own header and implementation files?

(I realize that this process started well before this patch, but as the purpose of this patch is to move declarations to more suitable places, maybe we should use the opportunity to create a more suitable place instead of moving them to DataflowAnalysisContext.h, which isn't really a good home for them either.)

The common theme seems to be that these functions / classes all perform some operation on the AST, so maybe ASTOperations.h/.cpp? Not really a _great_ name, but I think it's still a lot better than putting this all together with the `DataflowAnalysisContext`.

https://github.com/llvm/llvm-project/pull/88534