Add NetworkSoundEventDef registration to SoundAPI

[KomradeSpectre]

What is it?

This PR adds a way for developers to register NetworkSoundEventDef instances to the r2apiContentPack via the SoundAPI along with a few sanity checks for good measure.

Why?

Currently under SoundAPI there is not a way to add in sounds that are network ready. This utilizes the content pack system to register these at runtime under the R2API content pack which will then allow them to be used with RoR2's EntitySoundManager class.

How do I use it?

Similar to ItemAPI or ArtifactAPI, there are two ways of properly adding a NetworkSoundEventDef.

1. SoundAPI.AddNetworkedSoundEvent(NetworkedSoundEventDef? networkSoundEventDef) - allows you to pass in your own NetworkSoundEventDef to SoundAPI and if it passes the sanity checks, into the r2apiContentPack. Useful for when you want to save a reference to said NetworkSoundEventDef which you can grab the event ID from when you need to pass one into EntitySoundManager.

2. SoundAPI.AddNetworkedSoundEvent(string eventName) - Allows you to pass in the name of the WWise sound event and SoundAPI will create its own NetworkSoundEventDef from it. If this passes the sanity checks, it is also added into the r2apiContentPack. This is less useful, as you will have to provide the eventID to EntitySoundManager when you go to emit the sound via it.

[KomradeSpectre]

Noted, will change.

[tristanmcpherson]

Looks good! I reviewed it earlier but was waiting for others