Add modulo and mod as doc aliases for rem_euclid.

When I was learning Rust I looked for “a modulo function” and couldn’t
find one, so thought I had to write my own; it wasn't at all obvious
that a function with “rem” in the name was the function I wanted.
Hopefully this will save the next learner from that.

However, it does have the disadvantage that the top results in rustdoc
for “mod” are now these aliases instead of the Rust keyword, which
probably isn't ideal.

library/core/src/num/int_macros.rs

@@ -2126,6 +2126,7 @@ macro_rules! int_impl {
         /// assert_eq!(a.rem_euclid(-b), 3);
         /// assert_eq!((-a).rem_euclid(-b), 1);
         /// ```
+        #[doc(alias = "modulo", alias = "mod")]
         #[stable(feature = "euclidean_division", since = "1.38.0")]
         #[rustc_const_stable(feature = "const_euclidean_int_methods", since = "1.52.0")]
         #[must_use = "this returns the result of the operation, \

library/core/src/num/uint_macros.rs

@@ -2024,6 +2024,7 @@ macro_rules! uint_impl {
         /// ```
         #[doc = concat!("assert_eq!(7", stringify!($SelfT), ".rem_euclid(4), 3); // or any other integer type")]
         /// ```
+        #[doc(alias = "modulo", alias = "mod")]
         #[stable(feature = "euclidean_division", since = "1.38.0")]
         #[rustc_const_stable(feature = "const_euclidean_int_methods", since = "1.52.0")]
         #[must_use = "this returns the result of the operation, \

library/std/src/f32.rs

@@ -321,6 +321,7 @@ impl f32 {
     /// // limitation due to round-off error
     /// assert!((-f32::EPSILON).rem_euclid(3.0) != 0.0);
     /// ```
+    #[doc(alias = "modulo", alias = "mod")]
     #[rustc_allow_incoherent_impl]
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[inline]

library/std/src/f64.rs

@@ -321,6 +321,7 @@ impl f64 {
     /// // limitation due to round-off error
     /// assert!((-f64::EPSILON).rem_euclid(3.0) != 0.0);
     /// ```
+    #[doc(alias = "modulo", alias = "mod")]
     #[rustc_allow_incoherent_impl]
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[inline]