[clang] Rename the IR ops for `StackSaveOp` and `StackRestoreOp` (PR #179012)

[Andy Kaylor via cfe-commits]

https://github.com/andykaylor requested changes to this pull request.

The documentation is currently being generated from the incubator, but when these operations were upstreamed we made an intentional decision to remove the underscore. See https://github.com/llvm/llvm-project/pull/136426

We probably do something very soon to generate documentation from the upstream dialect definitions.

https://github.com/llvm/llvm-project/pull/179012