[Attributor] Cleanup and upstream `Attribute::MaxObjectSize`

We introduced a new llvm::Attribute in the Attributor tutorial (https://youtu.be/HVvvCSSLiTw) which never made it out of the prototype stage: https://github.com/jdoerfert/llvm-project/tree/feature/max_obj_size

The meaning of the attribute is described in the tutorial along with the rational, what code is there, and what needs to be done (to some degree).

• Write a short RFC for a the attribute and send it to llvm-dev
• Create the attribute with all the pluming (taken from the prototype)
• Extract the deduction code from the prototype, rebase it, cleanup and additional tests, put it up for review
• Extract the alias analysis interaction code, rebase it, cleanup and additional tests, put it up for review
• Determine if and how we can use assumed information of dereferenceability and max object size inside of AANoAlias.