Custom AudioStreams documentation refers to function which does not exist

**Your Godot version:**
4.0.3

**Issue description:**
I'm attempting to use GDExtension to add a custom audio stream, which is well documented for a module at this page. However, the page references AudioServer::get_singleton()->audio_data_alloc, which I cannot find in any Godot source or in the C++ binding.

I've done a full grep of every cpp file in both, with no results.

I suspect it was removed or replaced at some point, but I'm not sure by what. Worse, I've only got the name to tell me what it's doing; nothing to tell me how this is different from any other allocation. I'll have to go through old code, maybe, to figure it out.

**URL to the documentation page:**
https://docs.godotengine.org/en/stable/contributing/development/core_and_modules/custom_audiostreams.html

I unfortunately do not know what the correct information would be, so I am unable to open a pull request to fix it, myself, at this time. All help is much appreciated.