Revamp interpolation quality for resampling

[sakertooth]

When resampling audio, it was common for us to:

1. Use the SRC_LINEAR converter type only
2. Have no reasonable way to change this in the user settings
3. Have no way to ensure that the type specified was consistent across all our clients that use SRC_STATE to resample.

This PR addresses these concerns by:

1. Move all owners of raw SRC_STATE's to use the AudioResampler libsamplerate wrapper
2. Make the interpolation function in the export dialog actually apply for every AudioResampler
3. Allow the user to specify the interpolation mode that they wish to use on playback.

This also addresses the issue where pitch bending would cause major aliasing and audible "crackles" since linear interpolation was being used. The user can now choose an appropriate interpolation mode to avoid this from happening.

The functions in interpolation.h could've been used for this, but it was simpler to continue using libsamplerate for the time being, though it may be worth exploring the use of these functions instead of libsamplerate in the future. The code that currently uses these for resampling were left alone (e.g., VibratingString::resample was untouched).

[sakertooth]

I'm going to try and remove libsamplerate from this as well and use the functions within interpolation.h. I also don't know if we should even have a linear option anymore, given the aliasing that it brings to the audio.