[clang] SSAF JSON Format (PR #180021)

[Aviral Goel via cfe-commits]

aviralg wrote:

An example error message produced by this implementation looks like this:

```
reading TUSummary from file '/var/folders/ff/db1s_yhn41x6d_lltvzs5mz00000gp/T/json-format-test-cbf6b5/test.json'
reading SummaryData entries from field 'data'
reading SummaryData entry from index '0'
reading EntitySummary entries from field 'summary_data'
reading EntitySummary entry from index '0'
reading EntitySummary from field 'entity_summary'
missing or invalid 'second' field at index 0
```


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