[llvm] [mlir] [mlir] Mark `isa/dyn_cast/cast/...` member functions deprecated. (PR #90413)

[Christian Sigg via llvm-commits]

chsigg wrote:

The [Windows build](https://lab.llvm.org/buildbot/#/builders/216/builds/38157) that caused problems previously is still [passing](https://lab.llvm.org/buildbot/#/builders/216/builds/38322) after this change.

https://github.com/llvm/llvm-project/pull/90413