Reformat use declarations.

The previous commit updated `rustfmt.toml` appropriately. This commit is
the outcome of running `x fmt --all` with the new formatting options.

compiler/rustc_index/src/lib.rs

@@ -12,9 +12,10 @@ mod idx;
 mod slice;
 mod vec;
 
-pub use {idx::Idx, slice::IndexSlice, vec::IndexVec};
-
+pub use idx::Idx;
 pub use rustc_index_macros::newtype_index;
+pub use slice::IndexSlice;
+pub use vec::IndexVec;
 
 /// Type size assertion. The first argument is a type and the second argument is its expected size.
 ///