[llvm] [lit] Add JSON diffing support to lit (PR #177513)

[Aviral Goel via llvm-commits]

aviralg wrote:

> > I am working on two projects (one is being upstreamed as we speak and the other will be upstreamed in the future) that produce JSON files and use lit for testing.
> 
> What projects?

And this - https://discourse.llvm.org/t/rfc-emitting-auditable-sarif-logs-from-clang/88624

https://github.com/llvm/llvm-project/pull/177513