Rollup merge of rust-lang#92600 - asquared31415:float-must-use, r=joshtriplett

Add some missing `#[must_use]` to some `f{32,64}` operations

This PR adds `#[must_use]` to the following methods:
 - `f32::recip`
 - `f32::max`
 - `f32::min`
 - `f32::maximum`
 - `f32::minimum`
 and their equivalents in `f64`.
 These methods all produce a new value without modifying the original and so are pointless to call without using the result.

Author: ehuss

library/core/src/num/f32.rs

@@ -628,6 +628,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use = "this returns the result of the operation, without modifying the original"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn recip(self) -> f32 {
@@ -684,6 +685,7 @@ impl f32 {
     /// ```
     ///
     /// If one of the arguments is NaN, then the other argument is returned.
+    #[must_use = "this returns the result of the comparison, without modifying either input"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn max(self, other: f32) -> f32 {
@@ -703,6 +705,7 @@ impl f32 {
     /// ```
     ///
     /// If one of the arguments is NaN, then the other argument is returned.
+    #[must_use = "this returns the result of the comparison, without modifying either input"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn min(self, other: f32) -> f32 {
@@ -726,6 +729,7 @@ impl f32 {
     /// If one of the arguments is NaN, then NaN is returned. Otherwise this returns the greater
     /// of the two numbers. For this operation, -0.0 is considered to be less than +0.0.
     /// Note that this follows the semantics specified in IEEE 754-2019.
+    #[must_use = "this returns the result of the comparison, without modifying either input"]
     #[unstable(feature = "float_minimum_maximum", issue = "91079")]
     #[inline]
     pub fn maximum(self, other: f32) -> f32 {
@@ -757,6 +761,7 @@ impl f32 {
     /// If one of the arguments is NaN, then NaN is returned. Otherwise this returns the lesser
     /// of the two numbers. For this operation, -0.0 is considered to be less than +0.0.
     /// Note that this follows the semantics specified in IEEE 754-2019.
+    #[must_use = "this returns the result of the comparison, without modifying either input"]
     #[unstable(feature = "float_minimum_maximum", issue = "91079")]
     #[inline]
     pub fn minimum(self, other: f32) -> f32 {

library/core/src/num/f64.rs

@@ -643,6 +643,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use = "this returns the result of the operation, without modifying the original"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn recip(self) -> f64 {
@@ -700,6 +701,7 @@ impl f64 {
     /// ```
     ///
     /// If one of the arguments is NaN, then the other argument is returned.
+    #[must_use = "this returns the result of the comparison, without modifying either input"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn max(self, other: f64) -> f64 {
@@ -719,6 +721,7 @@ impl f64 {
     /// ```
     ///
     /// If one of the arguments is NaN, then the other argument is returned.
+    #[must_use = "this returns the result of the comparison, without modifying either input"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn min(self, other: f64) -> f64 {
@@ -742,6 +745,7 @@ impl f64 {
     /// If one of the arguments is NaN, then NaN is returned. Otherwise this returns the greater
     /// of the two numbers. For this operation, -0.0 is considered to be less than +0.0.
     /// Note that this follows the semantics specified in IEEE 754-2019.
+    #[must_use = "this returns the result of the comparison, without modifying either input"]
     #[unstable(feature = "float_minimum_maximum", issue = "91079")]
     #[inline]
     pub fn maximum(self, other: f64) -> f64 {
@@ -773,6 +777,7 @@ impl f64 {
     /// If one of the arguments is NaN, then NaN is returned. Otherwise this returns the lesser
     /// of the two numbers. For this operation, -0.0 is considered to be less than +0.0.
     /// Note that this follows the semantics specified in IEEE 754-2019.
+    #[must_use = "this returns the result of the comparison, without modifying either input"]
     #[unstable(feature = "float_minimum_maximum", issue = "91079")]
     #[inline]
     pub fn minimum(self, other: f64) -> f64 {