[Tracking] Re-implement existing bevy_audio examples

[SolarLiner]

Summary

Re-implementing examples is a good smoke test for feature-parity with the existing bevy_audio plugin.

• audio.rs Recreate audio and decodable/custom_sound examples from bevy_audio #17
• audio_control.rs Recreate audio_control example #9
• decodable.rs -> rename to "custom_sound" Recreate audio and decodable/custom_sound examples from bevy_audio #17
• pitch.rs
• soundtrack.rs
• spatial_audio_2d.rs
• spatial_audio_3d.rs