Auto merge of rust-lang#124959 - prorealize:update-result-documentation, r=joboet

Refactor examples and enhance documentation in result.rs

- Replaced `map` with `map_err` in the error handling example for correctness
- Reordered example code to improve readability and logical flow
- Added assertions to examples to demonstrate expected outcomes

Author: bors

library/core/src/result.rs

@@ -45,25 +45,29 @@
 //! that make working with it more succinct.
 //!
 //! ```
+//! // The `is_ok` and `is_err` methods do what they say.
 //! let good_result: Result<i32, i32> = Ok(10);
 //! let bad_result: Result<i32, i32> = Err(10);
-//!
-//! // The `is_ok` and `is_err` methods do what they say.
 //! assert!(good_result.is_ok() && !good_result.is_err());
 //! assert!(bad_result.is_err() && !bad_result.is_ok());
 //!
-//! // `map` consumes the `Result` and produces another.
+//! // `map` and `map_err` consume the `Result` and produce another.
 //! let good_result: Result<i32, i32> = good_result.map(|i| i + 1);
-//! let bad_result: Result<i32, i32> = bad_result.map(|i| i - 1);
+//! let bad_result: Result<i32, i32> = bad_result.map_err(|i| i - 1);
+//! assert_eq!(good_result, Ok(11));
+//! assert_eq!(bad_result, Err(9));
 //!
 //! // Use `and_then` to continue the computation.
 //! let good_result: Result<bool, i32> = good_result.and_then(|i| Ok(i == 11));
+//! assert_eq!(good_result, Ok(true));
 //!
 //! // Use `or_else` to handle the error.
 //! let bad_result: Result<i32, i32> = bad_result.or_else(|i| Ok(i + 20));
+//! assert_eq!(bad_result, Ok(29));
 //!
 //! // Consume the result and return the contents with `unwrap`.
 //! let final_awesome_result = good_result.unwrap();
+//! assert!(final_awesome_result)
 //! ```
 //!
 //! # Results must be used