[clang] [clang][dataflow] Allow `DataflowAnalysisContext` to use a non-owned `Solver`. (PR #91316)

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martinboehme wrote:

@joker-eph 

PS I don't see a revert of this PR, but I do see a revert of a different PR [here](https://github.com/llvm/llvm-project/commit/341aecc2dd0f6debcbe9f251a6d2e8a60d327eea), and that PR does look as if it could be the culprit.

Maybe you commented on this PR by mistake?

https://github.com/llvm/llvm-project/pull/91316