[llvm] [NFC][TableGen] Emit more readable builtin string table. (PR #105445)

[Rahul Joshi via llvm-commits]

jurahul wrote:

> The StringRef change should be a separate PR an come with some tests

I might have guessed :) The tests will just for rbegin()/rend(), right? I'll factor that out. 

https://github.com/llvm/llvm-project/pull/105445