Editorial: Define + use StringToNumber (#1554)

Introduce the abstract operation StringToNumber
to replace the prose that expressed the procedure
for applying ToNumber to String values.

spec.html

@@ -4793,7 +4793,7 @@ <h1>
               String
             </td>
             <td>
-              See grammar and conversion algorithm below.
+              Return ! StringToNumber(_argument_).
             </td>
           </tr>
           <tr>
@@ -4830,7 +4830,7 @@ <h1>
 
       <emu-clause id="sec-tonumber-applied-to-the-string-type">
         <h1>ToNumber Applied to the String Type</h1>
-        <p>ToNumber applied to Strings applies the following grammar to the input String interpreted as a sequence of UTF-16 encoded code points (<emu-xref href="#sec-ecmascript-language-types-string-type"></emu-xref>). If the grammar cannot interpret the String as an expansion of |StringNumericLiteral|, then the result of ToNumber is *NaN*.</p>
+        <p>The abstract operation StringToNumber specifies how to convert a String value to a Number value, using the following grammar.</p>
         <h2>Syntax</h2>
         <emu-grammar type="definition">
           StringNumericLiteral :::
@@ -4884,9 +4884,27 @@ <h2>Syntax</h2>
           </ul>
         </emu-note>
 
+        <emu-clause id="sec-stringtonumber" type="abstract operation">
+          <h1>
+            StringToNumber (
+              _str_: a String,
+            )
+          </h1>
+          <dl class="header">
+            <dt>description</dt>
+            <dd>It returns a Number.</dd>
+          </dl>
+          <emu-alg>
+            1. Let _text_ be ! StringToCodePoints(_str_).
+            1. Let _literal_ be ParseText(_text_, |StringNumericLiteral|).
+            1. If _literal_ is a List of errors, return *NaN*.
+            1. Return StringNumericValue of _literal_.
+          </emu-alg>
+        </emu-clause>
+
         <emu-clause id="sec-runtime-semantics-stringnumericvalue" type="sdo" aoid="StringNumericValue" oldids="sec-runtime-semantics-mv-s">
           <h1>Runtime Semantics: StringNumericValue</h1>
-          <p>The conversion of a String to a Number value is similar overall to the determination of the Number value for a numeric literal (see <emu-xref href="#sec-literals-numeric-literals"></emu-xref>), but some of the details are different, so the process for converting a String numeric literal to a value of the Number type is given here.</p>
+          <p>The conversion of a |StringNumericLiteral| to a Number value is similar overall to the determination of the NumericValue of a |NumericLiteral| (see <emu-xref href="#sec-literals-numeric-literals"></emu-xref>), but some of the details are different.</p>
           <emu-grammar>StringNumericLiteral ::: StrWhiteSpace?</emu-grammar>
           <emu-alg>
             1. Return *+0*<sub>𝔽</sub>.