Rollup merge of #84256 - tspiteri:pretty-minus-zero, r=workingjubilee

doc: use U+2212 for minus sign in floating-point -0.0 remarks

Also remove plus sign in `-0.0 == +0.0` to make it a valid expression.

Author: Dylan-DPC

library/std/src/primitive_docs.rs

@@ -807,10 +807,10 @@ mod prim_tuple {}
 ///
 /// Additionally, `f32` can represent some special values:
 ///
-/// - -0.0: IEEE 754 floating point numbers have a bit that indicates their sign, so -0.0 is a
-///   possible value. For comparison `-0.0 == +0.0` is true but floating point operations can
-///   carry the sign bit through arithmetic operations. This means `-1.0 * 0.0` produces -0.0 and
-///   a negative number rounded to a value smaller than a float can represent also produces -0.0.
+/// - −0.0: IEEE 754 floating point numbers have a bit that indicates their sign, so −0.0 is a
+///   possible value. For comparison −0.0 = +0.0, but floating point operations can carry
+///   the sign bit through arithmetic operations. This means −0.0 × +0.0 produces −0.0 and
+///   a negative number rounded to a value smaller than a float can represent also produces −0.0.
 /// - [∞](#associatedconstant.INFINITY) and
 ///   [−∞](#associatedconstant.NEG_INFINITY): these result from calculations
 ///   like `1.0 / 0.0`.