Simplify livekit config so that cargo check Just Works (#21661)

Supersedes https://github.com/zed-industries/zed/pull/21653

This enables us to use `cargo test -p workspace` on macOS and Linux.

Note that the line diffs in `shared_screen.rs` are spurious, I just
re-ordered the `macos` and `cross-platform` modules to match the order
in the call crate.

Release Notes:

- N/A

.github/workflows/ci.yml

@@ -129,8 +129,9 @@ jobs:
         run: |
           cargo build --workspace --bins --all-features
           cargo check -p gpui --features "macos-blade"
-          cargo check -p workspace --features "livekit-cross-platform"
+          cargo check -p workspace
           cargo build -p remote_server
+          script/check-rust-livekit-macos
 
   linux_tests:
     timeout-minutes: 60
@@ -162,8 +163,10 @@ jobs:
       - name: Run tests
         uses: ./.github/actions/run_tests
 
-      - name: Build Zed
-        run: cargo build -p zed
+      - name: Build other binaries and features
+        run: |
+          cargo build -p zed
+          cargo check -p workspace
 
   build_remote_server:
     timeout-minutes: 60