Enable developer customers to access AudioSource at development time

[david-c-kline]

This change serializes the grabReleaseAudioSource and passNotchAudioSource AudioSource fields, so that developer customers can configure options such as AudioMixerGroup, spatialization and play on awake.

Fixes: #435

Verified in Unity editor by:

• Adding a single AudioSource to the slider in the HandInteractionExamplesScene
• Assigning the manually attached AudioSource to the Grab/Release and PassNotch fields (newly serialized)
• Playing the scene in the editor and moving the slider
• Noting
  • No additional AudioSource objects were added to the slider
  • Audio plays correctly
  • The expected AudioSource parameters are updated while interacting with the slider

[AMollis]

Signing off on changes.

@david-c-kline , can you please look into refactoring to use a single audio source? Looking at the history of the file (from our internal repository) looks like @MaxWang-MS added the two audio sources when they first created the file.

I've opened an issue to track refactoring the two audio sources.

• [FEATURE REQUEST] Refactor SliderSounds to use a single audio source. #438

[david-c-kline]

Signing off on changes.

@david-c-kline , can you please look into refactoring to use a single audio source? Looking at the history of the file (from our internal repository) looks like @MaxWang-MS added the two audio sources when they first created the file.

I've opened an issue to track refactoring the two audio sources.

• [FEATURE REQUEST] Refactor SlideSounds to use a single audio source. #438

Will do. One thing to note is that using a single audio source will cause the grab/release sounds to have their pitch altered based on the position of the slider thumb (the pass notch code sweeps the frequency of the audio source).

If we are ok with that, I will look into #438, otherwise, we should continue using two audio sources.