[llvm] [SystemZ] Expand and automate .insn directive coverage (PR #222031)

[Dominik Steenken via llvm-commits]

dominik-steenken wrote:

This has been updated. The Opt-specific `.insn` definitions are gone and replaced by `NumOptionalOperands` in `InstSystemZ` and special parsing logic. I have also somewhat hardened the `SystemZInsnDirectiveEmitter` by moving more of the type definitions into the emitted code, reducing the amount of possible desynchronizations between what ois generated and what is written.

https://github.com/llvm/llvm-project/pull/222031