[llvm] Introduce paged vector (PR #66430)

[Vassil Vassilev via llvm-commits]

vgvassilev 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.

I think we need to add some test on the clang modules side. I am currently thinking how.. 

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