[llvm] [LangRef] Clarify that the pointer after an objet must be valid. (PR #127892)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Introduce a section for Allocated Objects, re-using parts of the Object Lifetime section.

I also updated various references to consistently refer to allocated objects. I could also split this off the a separate PR if preferred?

https://github.com/llvm/llvm-project/pull/127892