Adds a PPC for `any` and `all` as built-in operator syntax

[leonerd]

A reminder on the PPC process: Accepting this PR means we like the document, but it does not automatically imply that we accept the idea embodied by it. Accepting the document first is useful as it gives it a number and allows us to discuss and iterate on one canonical version of it, ahead of accepting the underlying idea. It is perfectly fine to accept the document even if questions and issues still surround it.