[llvm] [CODEOWNERS] Request notifications (PR #227742)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

> the notifications on PRs on which their review was explicitly requested in their inbox a bit difficult to manage.

The GitHub UI as a "review requested" filter already, although not sure if that's the complaint here.

I'm generally not a big fan of using `CODEOWNERS` just for notifications. Are you already/planning to review most of the PRs that touch these areas?

https://github.com/llvm/llvm-project/pull/227742