Make `bevy_audio` agnostic

## What problem does this solve or what need does it fill?

- Currently, there are several audio plugins in the bevy ecosystem, like:
- `bevy_audio`, uses rodio internally
- `bevy_kira_audio`, uses kira internally
- `bevy_oddio`, uses oddio internally
- There's also [`bevy_synthizer`], developed by Nolan#4103 on the [bevy discord](https://discord.com/channels/691052431525675048/749430447326625812/1007254460986302494)
- Making bevy plugins for audio stuff is hard, see [here](https://github.com/harudagondi/bevy_fundsp/blob/refactor-0.2/src/backend.rs), and PR for `bevy_fundsp` here: harudagondi/bevy_fundsp#6
- Like how `wgpu` have many backends abstracted away, I think `bevy_audio` should do the same.

[`bevy_synthizer`]: https://labs.lightsout.games/projects/bevy_synthizer

## What solution would you like?

- Majority of the types in `bevy_audio` should be converted into traits
- `Audio` will be a trait that supports playing audio with the given settings
- `AudioSource` will be a trait that holds static data, and have a `new` or `init` static method
- `AudioSink` is a trait that has basic methods for playing or pausing audio (plus some other niceties like in bevyengine/bevy#5828)
- `AudioPlugin` should hold its own backend, like what I did in [`bevy_fundsp`](https://github.com/harudagondi/bevy_fundsp/blob/1fbc33301c23d02636875a5dd1a51cc94eb9f5b8/src/lib.rs#L23-L30)

- A default backend for rodio, implemented in bevy_audio, or a separate `bevy_rodio` crate
- Bevy audio plugins that are just backends implement the traits in `bevy_audio` and should just work

I don't really know what the exact implementation would look like, but I do know it probably would have a bunch of trait magic and generics, sooo

## What alternative(s) have you considered?

- Do not do this. Just let third party audio plugins replace `bevy_audio` outright.
- As mentioned before, this will make the creation of third party audio plugins that isn't replacing bevy_audio very boilerplatey and kinda hard, as you'll have to make your code work on every audio plugin, and each plugin is very different.
- Do not remove the original types, but create several traits as mentioned above, and make rodio the default in bevy_audio
- using third party audio plugins will have both rodio, and kira for example, compiled in the same crate, which is not ideal, especially if rodio will not be used in the first place

## Additional context

- I'm working on harudagondi/bevy_fundsp#6
- Making your own `Backend` trait to support different plugins is kinda frustrating
- UPDATE (2022/11/12): I have written a [pre-RFC](https://hackmd.io/@harudagondi/rJK58vaWj) for this, and I'm currently prototyping a new library.