[llvm] [TableGen] Migrate LLVM RISCVTarget/VT Emitters to const RecordKeeper (PR #107697)

[Rahul Joshi via llvm-commits]

jurahul wrote:

part of https://discourse.llvm.org/t/psa-planned-changes-to-tablegen-getallderiveddefinitions-api-potential-downstream-breakages/81089

https://github.com/llvm/llvm-project/pull/107697