[mlir] Migrate away from ArrayRef(std::nullopt) (NFC)#145140

kazutakahirata merged 1 commit intollvm:mainllvm/llvm-project:mainfrom

kazutakahirata:cleanup_20250620_nullopt_mlirkazutakahirata/llvm-project:cleanup_20250620_nullopt_mlirCopy head branch name to clipboard