[llvm] [NFC][TableGen] Refactor JSON and detailed record emitter (PR #105770)

[Sergei Barannikov via llvm-commits]

https://github.com/s-barannikov approved this pull request.

LGTM
A note for the future: it would be much easier to review if formatting changes like variable renaming were in a separate commin (not necessarily in separate PR).

https://github.com/llvm/llvm-project/pull/105770