[lldb] [clang] [llvm] [mlir] [libc] [NFC][ObjectSizeOffset] Use classes instead of std::pair (PR #76882)

[Johannes Doerfert via cfe-commits]

https://github.com/jdoerfert approved this pull request.

I left one more comment. I think the new classes are clearly superior to the pairs. I looked over the changes, nothing jumps out. LG

https://github.com/llvm/llvm-project/pull/76882