[clang] [CIR] Fold ComplexRealOp from ComplexCreateOp (PR #147592)

[Henrich Lauko via cfe-commits]

xlauko wrote:

I don't see real use of not allowing this by default, as this is essentially identity folding, not really optimization?
And applying folds is way cheaper then rewrite patterns later.

Though yes, I agree we should have discussion where is the borderline, for instance `UnaryOp::fold` is doing more simplification/rewrite than this from my point of view.

https://github.com/llvm/llvm-project/pull/147592