[clang] [clang][dataflow] Change `diagnoseFunction` to take type of diagnostic list instead of diagnostic itself. (PR #66014)

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martinboehme wrote:

> Updated to enforce llvm::SmallVector, per Martin's recommendation. PTAL.

LGTM, but note that the PR title is now out of date.



https://github.com/llvm/llvm-project/pull/66014