Full OscillatorNode support

[ferjm]

Right now we implement only the generation of sine waves, but there are other sine wave types that we need to implement, including the periodic waveform. This is not a high priority at the moment though.

[jdm]

I am reserving this for a group of NCSU students to work on.

[jdm]

media/audio/src/oscillator_node.rs

Line 120 in 3292937

let value = vol * f32::sin(NumCast::from(self.phase).unwrap());

[ferjm]

Part of this work was completed in #163. The remaining bits are tracked in servo/servo#22364