Use field init shorthand where possible

Field init shorthand allows writing initializers like `tcx: tcx` as
`tcx`. The compiler already uses it extensively. Fix the last few places
where it isn't yet used.

compiler/rustc_const_eval/src/interpret/projection.rs

@@ -325,7 +325,7 @@ where
         let actual_to = if from_end {
             if from.checked_add(to).is_none_or(|to| to > len) {
                 // This can only be reached in ConstProp and non-rustc-MIR.
-                throw_ub!(BoundsCheckFailed { len: len, index: from.saturating_add(to) });
+                throw_ub!(BoundsCheckFailed { len, index: from.saturating_add(to) });
             }
             len.checked_sub(to).unwrap()
         } else {