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

[Bill Wendling via cfe-commits]

bwendling wrote:

> I am unsure I understand why we do the base template rather than inheritance. Where is the base template used? If we do inheritance we could avoid duplicating of members and provide default impls that work with many things, e.g., all operator== are the same.

I made these templates because they're dealing with different types. I can try to avoid duplicating the comparison functions, but I don't know if we'll get much out of inheritance that we don't get with templates...or really just different structs.

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