Rollup merge of #94838 - antonok-edm:float-parse-docs, r=Dylan-DPC

Make float parsing docs more comprehensive

I was working on some code with some specialized restrictions on float parsing. I noticed the doc comments for `f32::from_str` and `f64::from_str` were missing several cases of valid inputs that are otherwise difficult to discover without looking at source code.

I'm not sure if the doc comments were initially intended to contain a comprehensive description of valid inputs, but I figured it's useful to include these extra cases for reference.

library/core/src/num/dec2flt/mod.rs

@@ -112,21 +112,24 @@ macro_rules! from_str_float_impl {
             /// * '2.5E-10'
             /// * '5.'
             /// * '.5', or, equivalently, '0.5'
-            /// * 'inf', '-inf', 'NaN'
+            /// * 'inf', '-inf', '+infinity', 'NaN'
+            ///
+            /// Note that alphabetical characters are not case-sensitive.
             ///
             /// Leading and trailing whitespace represent an error.
             ///
             /// # Grammar
             ///
-            /// All strings that adhere to the following [EBNF] grammar
-            /// will result in an [`Ok`] being returned:
+            /// All strings that adhere to the following [EBNF] grammar when
+            /// lowercased will result in an [`Ok`] being returned:
             ///
             /// ```txt
-            /// Float  ::= Sign? ( 'inf' | 'NaN' | Number )
+            /// Float  ::= Sign? ( 'inf' | 'infinity' | 'nan' | Number )
             /// Number ::= ( Digit+ |
+            ///              '.' Digit* |
             ///              Digit+ '.' Digit* |
             ///              Digit* '.' Digit+ ) Exp?
-            /// Exp    ::= [eE] Sign? Digit+
+            /// Exp    ::= 'e' Sign? Digit+
             /// Sign   ::= [+-]
             /// Digit  ::= [0-9]
             /// ```