Add links from assert_eq! docs to debug_assert_eq!, etc.

This adds information and links from the docs for the following macros to their debug-only versions:

* `assert_eq!`
* `assert_ne!`
* `assert_matches!`

This matches the existing documentation for the `assert!` macro.

library/core/src/macros/mod.rs

@@ -14,6 +14,12 @@ macro_rules! panic {
 
 /// Asserts that two expressions are equal to each other (using [`PartialEq`]).
 ///
+/// Assertions are always checked in both debug and release builds, and cannot
+/// be disabled. See [`debug_assert_eq!`] for assertions that are disabled in
+/// release builds by default.
+///
+/// [`debug_assert_eq!`]: crate::debug_assert_eq
+///
 /// On panic, this macro will print the values of the expressions with their
 /// debug representations.
 ///
@@ -64,6 +70,12 @@ macro_rules! assert_eq {
 
 /// Asserts that two expressions are not equal to each other (using [`PartialEq`]).
 ///
+/// Assertions are always checked in both debug and release builds, and cannot
+/// be disabled. See [`debug_assert_ne!`] for assertions that are disabled in
+/// release builds by default.
+///
+/// [`debug_assert_ne!`]: crate::debug_assert_ne
+///
 /// On panic, this macro will print the values of the expressions with their
 /// debug representations.
 ///
@@ -122,6 +134,12 @@ macro_rules! assert_ne {
 /// optional if guard can be used to add additional checks that must be true for the matched value,
 /// otherwise this macro will panic.
 ///
+/// Assertions are always checked in both debug and release builds, and cannot
+/// be disabled. See [`debug_assert_matches!`] for assertions that are disabled in
+/// release builds by default.
+///
+/// [`debug_assert_matches!`]: crate::assert_matches::debug_assert_matches
+///
 /// On panic, this macro will print the value of the expression with its debug representation.
 ///
 /// Like [`assert!`], this macro has a second form, where a custom panic message can be provided.