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

[via cfe-commits]

================
@@ -245,10 +245,10 @@ runDataflowAnalysis(
 ///   iterations.
 /// - This limit is still low enough to keep runtimes acceptable (on typical
 ///   machines) in cases where we hit the limit.
-template <typename AnalysisT, typename Diagnostic>
-llvm::Expected<std::vector<Diagnostic>> diagnoseFunction(
+template <typename AnalysisT, typename DiagnosticList>
+llvm::Expected<DiagnosticList> diagnoseFunction(
----------------
martinboehme wrote:

```suggestion
template <typename AnalysisT, typename Diagnostic>
llvm::Expected<llvm::SmallVector<Diagnostic>> diagnoseFunction(
```

See also PR-level comment with rationale.

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