[clang] [clang][ssaf] Implement JSONFormat (PR #180021)

[Aviral Goel via cfe-commits]

aviralg wrote:

We discovered an order-related bug in `normalizeTUSummaryJSON` that happens in the presence of multiple summaries.We serialize `std::map` to JSON `array` whose iteration order is unspecified. This causes the TUSummary JSON representations to differ even though they are "equivalent". A follow-up PR will fix this issue in the test fixture.

https://github.com/llvm/llvm-project/pull/180021