Avoid &format("...") calls in error message code.

Error message all end up passing into a function as an `impl
Into<{D,Subd}iagnosticMessage>`. If an error message is creatd as
`&format("...")` that means we allocate a string (in the `format!`
call), then take a reference, and then clone (allocating again) the
reference to produce the `{D,Subd}iagnosticMessage`, which is silly.

This commit removes the leading `&` from a lot of these cases. This
means the original `String` is moved into the
`{D,Subd}iagnosticMessage`, avoiding the double allocations. This
requires changing some function argument types from `&str` to `String`
(when all arguments are `String`) or `impl
Into<{D,Subd}iagnosticMessage>` (when some arguments are `String` and
some are `&str`).

compiler/rustc_driver_impl/src/args.rs

@@ -25,7 +25,7 @@ pub fn arg_expand_all(at_args: &[String]) -> Vec<String> {
             Ok(arg) => args.extend(arg),
             Err(err) => rustc_session::early_error(
                 rustc_session::config::ErrorOutputType::default(),
-                &format!("Failed to load argument file: {err}"),
+                format!("Failed to load argument file: {err}"),
             ),
         }
     }