Add types and support 8.4

[nickdnk]

This is a fairly large refactor. I have:

1. Added types to everything I could find within the scope of PHP 8.1.
2. Added way more properties to known objects (but this would require some effort/help from others as the Graph API is huge).
3. Added support for properly casting arrays and edges to their correct GraphNode subclasses.
4. Remove a lot of legacy things, such as a custom autoload.php, PHP 5.5 BC todos, outdated documentation
5. Removed "helper" methods that would duplicate all the type-casting since I added way more objects/types.

I will be releasing this as a 8.0.0-rc1 and have it collect some feedback. If you just use this to "log in with Facebook" it is very unlikely that you would need to change anything, but please see the changelog for details.