rls no longer builds after rust-lang/rust#78334

[rust-highfive]

Hello, this is your friendly neighborhood mergebot.
After merging PR #78334, I observed that the tool rls no longer builds.
A follow-up PR to the repository https://github.com/rust-lang/rls is needed to fix the fallout.

cc @jonas-schievink, do you think you would have time to do the follow-up work?
If so, that would be great!

[calebcartwright]

Believe root cause is recent changes made in rustc_data_structures which is in the rustfmt dep tree from our rustc-ap-* usage. Should be sorted after our next rustc-ap bump in rustfmt, more details in #78341 (comment)