[mlir][LLVM][GPU] Migrate to explicit split inherent/discardable attribute APIs access (#218921)

Use discardable attribute APIs and typed operation accessors throughout
the LLVM and GPU dialect families, their conversions, translations, and
tests.

Assisted-by: Codex
GitOrigin-RevId: 96cb9c493b96f1ddf0c47c3bb7c1195b88148ec7