[JSC] Use Identifier::from in IdentifierArena::makeNumericIdentifier

https://bugs.webkit.org/show_bug.cgi?id=259959
rdar://113598301

Reviewed by Keith Miller.

We should just use Identifier::from from IdentifierArena::makeNumericIdentifier, which can have some optimization additionally via per-VM string cache.
Also, we can use `canBeInt32` to check wether we can stringify it as int32_t instead of double, which is much faster.

* Source/JavaScriptCore/parser/ParserArena.h:
(JSC::IdentifierArena::makeNumericIdentifier):

Canonical link: https://commits.webkit.org/266743@main

Source/JavaScriptCore/parser/ParserArena.h

@@ -133,9 +133,13 @@ namespace JSC {
 
     inline const Identifier& IdentifierArena::makeNumericIdentifier(VM& vm, double number)
     {
-        // FIXME: Why doesn't this use the Identifier::from overload that takes a double?
-        // Seems we are missing out on multiple optimizations by not using it.
-        m_identifiers.append(Identifier::fromString(vm, String::number(number)));
+        Identifier token;
+        // This is possible that number can be -0, but it is OK since ToString(-0) is "0".
+        if (canBeInt32(number))
+            token = Identifier::from(vm, static_cast<int32_t>(number));
+        else
+            token = Identifier::from(vm, number);
+        m_identifiers.append(WTFMove(token));
         return m_identifiers.last();
     }