Add FRAC_1_SQRT_2PI doc alias to FRAC_1_SQRT_TAU

This is create symmetry between the already existing TAU constant (2pi)
and the newly-introduced FRAC_1_SQRT_2PI, keeping the more common
name while increasing visibility.

library/core/src/num/f128.rs

@@ -69,6 +69,7 @@ pub mod consts {
         0.564189583547756286948079451560772585844050629328998856844086_f128;
 
     /// 1/sqrt(2π)
+    #[doc(alias = "FRAC_1_SQRT_TAU")]
     #[unstable(feature = "f128", issue = "116909")]
     // Also, #[unstable(feature = "more_float_constants", issue = "103883")]
     pub const FRAC_1_SQRT_2PI: f128 =

library/core/src/num/f16.rs

@@ -68,6 +68,7 @@ pub mod consts {
     pub const FRAC_1_SQRT_PI: f16 = 0.564189583547756286948079451560772586_f16;
 
     /// 1/sqrt(2π)
+    #[doc(alias = "FRAC_1_SQRT_TAU")]
     #[unstable(feature = "f16", issue = "116909")]
     // Also, #[unstable(feature = "more_float_constants", issue = "103883")]
     pub const FRAC_1_SQRT_2PI: f16 = 0.398942280401432677939946059934381868_f16;

library/core/src/num/f32.rs

@@ -328,6 +328,7 @@ pub mod consts {
     pub const FRAC_1_SQRT_PI: f32 = 0.564189583547756286948079451560772586_f32;
 
     /// 1/sqrt(2π)
+    #[doc(alias = "FRAC_1_SQRT_TAU")]
     #[unstable(feature = "more_float_constants", issue = "103883")]
     pub const FRAC_1_SQRT_2PI: f32 = 0.398942280401432677939946059934381868_f32;
 

library/core/src/num/f64.rs

@@ -328,6 +328,7 @@ pub mod consts {
     pub const FRAC_1_SQRT_PI: f64 = 0.564189583547756286948079451560772586_f64;
 
     /// 1/sqrt(2π)
+    #[doc(alias = "FRAC_1_SQRT_TAU")]
     #[unstable(feature = "more_float_constants", issue = "103883")]
     pub const FRAC_1_SQRT_2PI: f64 = 0.398942280401432677939946059934381868_f64;