E0046 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0046.rs

Error E0046 needs a span_label, updating it from:

error[E0046]: not all trait items implemented, missing: `foo`
  --> src/test/compile-fail/E0046.rs:17:1
   |
17 | impl Foo for Bar {} //~ ERROR E0046
   | ^^^^^^^^^^^^^^^^^^^

To:

error[E0046]: not all trait items implemented, missing: `foo`
  --> src/test/compile-fail/E0046.rs:17:1
   |
17 | impl Foo for Bar {} //~ ERROR E0046
   | ^^^^^^^^^^^^^^^^^^^ missing `foo` in implementation

[KiChjang]

Should be fixed by #35355.

[kali]

Not sure if this is the right place, but it would be great if the error message was giving the whole prototype of the missing methods, ready to be cut-and-pasted (scalac does it).

[sophiajt]

@kali - can you file a new issue with your suggestion and cc me?