Add ability read audio directly from audio playback instead of using the recording effect

[Faolan-Rad]

Describe the project you are working on

Networked vr creation tools

Describe the problem or limitation you are having in your project

User It is disgusting to have to add a audio player node to the scene set to a bus that then has a recorder in order to get the pcm audio data I would like to be able to instant a playback on a stream and just use the mixed method directly

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Makes it easier to use and more efficient to read mic input

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Make the mix method on AudioStreamPlayback where it can be called from gd extensions and c#

If this enhancement will not be used often, can it be worked around with a few lines of script?

I would rather just not use the godot audio at that point and use openal if i have to go through a lot of hoops just to get mic input

Is there a reason why this should be core and not an add-on in the asset library?

Would make more scene for the method to be callable then writing a lot of code to work around it

[AThousandShips]

Essentially the same as:

• Expose more audio methods to be able to generate waveform previews #127