Implement NativeExtension pointer arguments

[reduz]

• Allows calling into native extensions directly with a pointer
• Makes it easier to implement some APIs more efficiently
• Appears with a "*" in the documentation for the argument.
• Implementing the pointer handling is entirely up to the implementation, although the extension API provides some hint.
• AudioStream has been implemented as an example, allowing to create NativeExtension based AudioStreams.

Example of how it looks:

GDVIRTUAL3(_mix, GDNativePtr<AudioFrame>, float, int)

[CedNaru]

So if I understand we can now directly send pointers to Godot by casting them to regular int64 by using this new hint.
Will that solve this proposal: godotengine/godot-proposals#3037 ?

When it comes to usability, not sure I really get the AudioStream example.
So in 3.x, this class could only be used/implemented in a module because it was making use of a pointer to an internal structure AudioFrame. But in 4.0, AudioStream is exposed in the API because of the new virtual bind and the _mix method "sees" an int in place of the AudioFrame pointer?

[reduz]

@CedNaru This is not a way to send generic pointers to Godot, it's a way for Godot to send generic pointer to native extensions. It's only meant for implementations using compiled languages to receive low level data required in some situations (like mixing audio, writing network data buffers, etc).

[reduz]

I also have no idea if it solves the proposal, the author did not make clear what the intention was with it.

[CedNaru]

Hum ok, so this PR won't solve it.
The intent was to send third-party library structs/classes pointers to Godot and store them in a variant for future use.
In other words, it's a way to replicate RID but for structs external to Godot.
But this PR is kinda the reverse of that.

[reduz]

@CedNaru as written in that proposal, you can cast to integer and back, its not very difficult and makes little difference.

[neikeq]

Are the AudioFrame members meant to be accessed by native extensions? If so how can they do this if they don't have the struct declaration?