Fix the Redefinition of 'NativeXXXSpecJSI' error with Frameworks (#44005)

Summary:

When using frameworks on iOS, there is a possibility that modules import the Spec.h file twice and this might end up in a Redefinition of some symbols and duplication of symbols which ends up in build errors, as reported here: #42670.

This change adds some [`#include guards`](https://en.wikipedia.org/wiki/Include_guard) in codegen to avoid the redefinition of those symbols if the header is imported/included multiple times.

Note: I also experimented with `#pragma once`, but it looks like Apple is not happy with that directive. [It seems](https://forums.developer.apple.com/forums/thread/739964) that it started working flakely from Xcode 15.

## Changelog:
[General][Fixed] - Make sure that we can't include Codegen symbols multiple times

Differential Revision: D55925605

Author: cipolleschi