Auto merge of #131859 - chriskrycho:update-trpl, r=onur-ozkan

Update TRPL to add new Chapter 17: Async and Await

- Add support to `rustbook` to pass through the `-L`/`--library-path` flag to `mdbook` so that references to the `trpl` crate
- Build the `trpl` crate as part of the book tests. Make it straightforward to add other such book dependencies in the future if needed by implementing that in a fairly general way.
- Update the submodule for the book to pull in the new chapter on async and await, as well as a number of other fixes. This will happen organically/automatically in a week, too, but this lets me group this change with the next one:
- Update the compiler messages which reference the existing chapters 17–20, which are now chapters 18-21. There are only two, both previously referencing chapter 18.
- Update the UI tests which reference the compiler message outputs.

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