rls no longer builds after rust-lang/rust#82929

[rust-highfive]

Hello, this is your friendly neighborhood mergebot.
After merging PR #82929, 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 @m-ou-se, do you think you would have time to do the follow-up work?
If so, that would be great!

[m-ou-se]

The error:

error[E0432]: unresolved import `cargo::core::enable_nightly_features`
  --> src/tools/rls/rls/src/build/cargo.rs:16:5
   |
16 |     enable_nightly_features, PackageId, Shell, Target, TargetKind, Verbosity, Workspace,
   |     ^^^^^^^^^^^^^^^^^^^^^^^ no `enable_nightly_features` in `core`

error[E0425]: cannot find function `enable_nightly_features` in module `cargo::core`
  --> src/tools/rls/rls/src/project_model.rs:48:22
   |
48 |         cargo::core::enable_nightly_features();
   |                      ^^^^^^^^^^^^^^^^^^^^^^^ not found in `cargo::core`

error: aborting due to 2 previous errors

[jyn514]

@Xanewok See rust-lang/cargo#9181, the way to do this now is to set config.nightly_features_allowed = true.

[jyn514]

Oh oops, you already opened rust-lang/rls#1723.