fix(interop): Correctly initialize pointers from numbers on 64-bit archs

JavaScript represents 64-bit integers as floating point `double` values.
This means that the conversion from JSValue to pointer is done by
extracting the `double` value and then converting it to integer.

**Caution:** This means that pointers with more than 54 significant bits
are likely to be rounded and misrepresented!
However, current OS and hardware implementations are using 48 bits,
so we're safe at the time being.
See https://en.wikipedia.org/wiki/X86-64#Virtual_address_space_details
and https://en.wikipedia.org/wiki/ARM_architecture#ARMv8-A

Author: mbektchiev

src/NativeScript/Marshalling/Pointer/PointerConstructor.cpp

@@ -33,7 +33,19 @@ void PointerConstructor::finishCreation(VM& vm, PointerPrototype* pointerPrototy
 EncodedJSValue JSC_HOST_CALL PointerConstructor::constructPointerInstance(ExecState* execState) {
     void* value = nullptr;
     if (execState->argumentCount() == 1) {
-        value = reinterpret_cast<void*>(execState->argument(0).toUInt32(execState));
+        auto arg0 = execState->argument(0);
+#if __SIZEOF_POINTER__ == 8
+        // JSC stores 64-bit integers as doubles in JSValue.
+        // Caution: This means that pointers with more than 54 significant bits
+        // are likely to be rounded and misrepresented!
+        // However, current OS and hardware implementations are using 48 bits,
+        // so we're safe at the time being.
+        // See https://en.wikipedia.org/wiki/X86-64#Virtual_address_space_details
+        // and https://en.wikipedia.org/wiki/ARM_architecture#ARMv8-A
+        value = reinterpret_cast<void*>(static_cast<int64_t>(arg0.toIntegerPreserveNaN(execState)));
+#else
+        value = reinterpret_cast<void*>(arg0.toInt32(execState));
+#endif
     }
 
     JSValue result = jsCast<GlobalObject*>(execState->lexicalGlobalObject())->interop()->pointerInstanceForPointer(execState, value);