Auto merge of #112407 - tgross35:ci-docs-publish, r=Mark-Simulacrum

Publish docs as github artifacts during CI

Discussed here: https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/Building.20docs.20for.20PR.20CI

The goal is to make docs available for download after CI runs on PRs, for easy review of API changes.

Notes:

- Currently this only captures library documentation (`core`, `alloc`, `std`, `test`, `proc_macro`)
- You can't see artifacts until the entire workflow run has completed actions/upload-artifact#53
- There is currently a generic file name `ci-artifacts`. No way to customize this based on contained files unfortunately actions/upload-artifact#349

You can find the results at the bottom of the CI "summary" page:

<img width="379" alt="image" src="https://github.com/rust-lang/rust/assets/13724985/d3748e59-242c-40f8-9f54-82177b9b481b">

Author: bors