[clang] [RFC] Initial implementation of P2719 (PR #113510)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

@cor3ntin @AaronBallman @erichkeane There is a bunch of super unpleasant nonsense in the new and delete codegen paths, it would simplify things a lot if we actually had the AST nodes actually be complete, e.g. the AST node would include expression nodes for the implicit parameters, etc. Unfortunately I don't know how that would deal with dependent types, because obviously `new DependentType` can't know the full set of implicit parameters. We *could* just construct all of them, and then have codegen simply evaluate the relevant ones, but I'm not sure if that is a valid/correct approach?

https://github.com/llvm/llvm-project/pull/113510