[clang] [clang][dataflow] Discard unneeded `ExprToLoc` and `ExprToVal` entries. (PR #72850)

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martinboehme wrote:

Update: Here's a draft implementation of the "simpler, bolder approach" referenced above:

https://github.com/llvm/llvm-project/pull/72985

The code is a _lot_ simpler -- it's mainly deleting code -- and I think I'm convinced at this point that this is the preferable thing to do. Would appreciate input.

If others agree, there's not a whole lot of work remaining on this draft -- main thing is to see how this affects SAT solver timeouts on real-world codebases (I expect the effect to be similar to this current patch) and some simplification in the code (converting two function templates to non-template functions because they now only get called with one specific set of argument types).

https://github.com/llvm/llvm-project/pull/72850