[clang] Introduce paged vector (PR #66430)

[Giulio Eulisse via cfe-commits]

ktf wrote:

@vgvassilev done.

@ChuanqiXu9 I think I addressed all your additional comments and updated the PR. Please let me know if you have further ones or if you want me to squash the commits into one.

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