[clang] [CIR] Split side_effect into memory effects, nounwind, and willreturn (PR #223890)

[Adam Smith via cfe-commits]

adams381 wrote:

I've pushed the version we landed on.  It is a CIR attribute again, so the CIR dialect no longer depends on the LLVM dialect.  The hand-rolled printer stays removed, so memory effects now print as the full six-field struct.

https://github.com/llvm/llvm-project/pull/223890