Replace uses of `isa`/`dyn_cast`/`cast`/... member functions

[jopperm]

We recently rebased on top of llvm/llvm-project#90413, causing many deprecation warnings across CIR's codebase. The use of mlir::Type's member functions should be mechanically replaced by the corresponding free functions.

[bcardosolopes]

We must! I wonder if MLIR folks used clang-tidy or something to fix that. It's also going to be annoying to enforce that during review, but hopefully folks are going to catch up fast.

[jopperm]

I'll look into it!