Add get_buffered_amount() to WebRTCDataChannel (Godot 3.x)

[dsnopek]

Godot 3.x version of PR #50658

[Faless]

If we want to backport this cleanly to 3.x (i.e. without breaking GDNative compatibility) we should probably use the next field:
https://github.com/godotengine/godot/blob/58ec58d5d0435d52c1a01ffeece35799ba3da533/modules/gdnative/include/net/godot_webrtc.h#L108-L110

And add a new godot_net_webrtc_peer_connection_ext struct with the new function, and a next pointer.
The plugin will then add the extra struct to the next pointer.

That way the old version of the plugin would still work with the new version of the engine.

[dsnopek]

Oh, cool! I didn't realize there was a mechanism in place for this. :-) I'll update this PR and the gdnative one to use that approach.

[dsnopek]

PR is now updated to preserve backcompat!

[Faless]

Great job!

[Faless]

Thanks!

[dsnopek]

Thanks for the review and speedy merge! :-)

I've made a PR to godot-headers that should allow the official GDNative plugin to build:

godotengine/godot-headers#94

[Faless]

Yeah, I was actually too hasty :(.
#define GODOT_NET_WEBRTC_API_MINOR should have been updated to 4 with this change.

And the master one should have been updated to:
#define GODOT_NET_WEBRTC_API_MAJOR 4
#define GODOT_NET_WEBRTC_API_MINOR 0

[dsnopek]

I just created these two PRs to fix those #define's:

• Godot 3.x: Update GDNative API version for changes from #50659 (Godot 3.x) #50706
• Godot 4.x: Update GDNative API version for changes from #50659 #50704