Add flatmap/flat_map -> and_then suggestions

Author: estebank

library/core/src/option.rs

@@ -1403,6 +1403,7 @@ impl<T> Option<T> {
     #[doc(alias = "flatmap")]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_confusables("flat_map", "flatmap")]
     pub fn and_then<U, F>(self, f: F) -> Option<U>
     where
         F: FnOnce(T) -> Option<U>,

library/core/src/result.rs

@@ -1315,6 +1315,7 @@ impl<T, E> Result<T, E> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_confusables("flat_map", "flatmap")]
     pub fn and_then<U, F: FnOnce(T) -> Result<U, E>>(self, op: F) -> Result<U, E> {
         match self {
             Ok(t) => op(t),