[clang-tools-extra] [clang-doc] add a JSON generator (PR #142483)

[Paul Kirth via cfe-commits]

ilovepi wrote:


> I'll investigate this. Although right off the bat, the names in the Infos aren't mangled. `Name` and `FullName` are the same for both records, which is unfortunate.

OK, well, let's give it a try, and if its too hard lets ... IDK go w/ the YAML thing, so its correct? Testing will be kind of hellish so I'm loathe to go that path, but if one is obviously broken, then we should probably avoid it. 

https://github.com/llvm/llvm-project/pull/142483