Auto merge of #6416 - deg4uss3r:map_err_restricted, r=ebroto

Moved map_err_ignore to restriction and updated help message

This MR moves map_err_ignore lint from `pedantic` to the `restriction` category of lints and updates the help message to give the user an option to ignore the lint by naming the closure variable e.g. `.map_err(|_ignored| ...`

---

changelog: move map_err_ignore to restriction category

tests/ui/map_err.rs

@@ -22,5 +22,9 @@ fn main() -> Result<(), Errors> {
 
     println!("{:?}", x.map_err(|_| Errors::Ignored));
 
+    // Should not warn you because you explicitly ignore the parameter
+    // using a named wildcard value
+    println!("{:?}", x.map_err(|_foo| Errors::Ignored));
+
     Ok(())
 }

tests/ui/map_err.stderr

@@ -1,11 +1,11 @@
-error: `map_err(|_|...` ignores the original error
+error: `map_err(|_|...` wildcard pattern discards the original error
   --> $DIR/map_err.rs:23:32
    |
 LL |     println!("{:?}", x.map_err(|_| Errors::Ignored));
    |                                ^^^
    |
    = note: `-D clippy::map-err-ignore` implied by `-D warnings`
-   = help: Consider wrapping the error in an enum variant
+   = help: Consider storing the original error as a source in the new error, or silence this warning using an ignored identifier (`.map_err(|_foo| ...`)
 
 error: aborting due to previous error