E0071 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0071.rs

Error E0071 needs a span_label, updating it from:

error[E0071]: `Foo::FirstValue` does not name a struct or a struct variant
  --> src/test/compile-fail/E0071.rs:14:13
   |
14 |     let u = Foo::FirstValue { value: 0 }; //~ ERROR E0071
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0071]: `u32` does not name a struct or a struct variant
  --> src/test/compile-fail/E0071.rs:15:13
   |
15 |     let t = u32 { value: 4 }; //~ ERROR E0071
   |             ^^^^^^^^^^^^^^^^

To:

error[E0071]: `Foo::FirstValue` does not name a struct or a struct variant
  --> src/test/compile-fail/E0071.rs:14:13
   |
14 |     let u = Foo::FirstValue { value: 0 }; //~ ERROR E0071
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not a struct

error[E0071]: `u32` does not name a struct or a struct variant
  --> src/test/compile-fail/E0071.rs:15:13
   |
15 |     let t = u32 { value: 4 }; //~ ERROR E0071
   |             ^^^^^^^^^^^^^^^^ not a struct

Bonus: The span should underline only the name of the thing that's not a struct rather than the whole expression. Example:

error[E0071]: `u32` does not name a struct or a struct variant
  --> src/test/compile-fail/E0071.rs:15:13
   |
15 |     let t = u32 { value: 4 }; //~ ERROR E0071
   |             ^^^ not a struct

This may require additional compiler changes.

[razielgn]

Booking this one, as mentioned in #35233.