[clang] Introduce paged vector (PR #66430)

[David Blaikie via cfe-commits]

dwblaikie wrote:

(aside: I was confused why there was only one commit in this PR, since there'd been so many updates to it - but I see they've been force pushed, which my vague understanding is that force pushing can complicate tracking previous comments and the LLVM convention is not to do so: "When updating a pull request, you should push additional “fix up” commits to your branch instead of force pushing. This makes it easier for GitHub to track the context of previous review comments. " - https://llvm.org/docs/GitHub.html#updating-pull-requests )

https://github.com/llvm/llvm-project/pull/66430