Switch to libsamplerate's callback API in Sample

[sakertooth]

This PR switches the use of libsamplerate in Sample to the callback API instead of the full API. This PR is great for many reasons:

1. Massive simplification of the audio processing in Sample. The Sample::advance function was removed as well as the heap allocation in Sample::play.
2. Since the heap allocation in Sample::play was removed, Sample::play should be more safe to call in real-time.
3. Don't know if anybody can notice this, but in current master, it sounds like some high frequency content in the playback was not being added compared to this PR. Using a marginSize of 64 fixed this in current master, but I wanted to try and improve this code further.

Other changes:

• I also added some fixes here and there (e.g., libsamplerate takes in the resampling ratio as a double, but it was originally being passed in as a float).
• I removed AudioResampler since it was no longer being used by anything, and it does not seem like a good idea for libsamplerate's usage in the codebase to be limited by the API of AudioResampler. The code should be allowed to choose which API from libsamplerate it wants to use.
• s_interpolationMargins is only used by GigInstrument currently, so I moved the array in there.

[sakertooth]

Forgot to apply amplification, fixing that now (as well as merge conflicts).

[Rossmaxx]

Since the heap allocation in Sample::play was removed, Sample::play is now safe to call in a real-time.

Does this got anything to do with the crashes I experience on #5990? Looks like it.

[sakertooth]

Does this got anything to do with the crashes I experience on #5990? Looks like it.

I don't think so. 5990 uses SampleRecordHandle's, which do not involve calling Sample::play. This is for processing samples and is used in the AFP, Patman, sample tracks, etc.

[messmerd]

I tested it and it seems to work pretty well

[messmerd]

Suggested change

	const auto state = static_cast<PlaybackState*>(callbackData);
	const auto& loop = *state->loop;
	const auto& sample = state->sample;
	auto& index = state->frameIndex;
	auto& backwards = state->backwards;
	const auto state = static_cast<PlaybackState*>(callbackData);
	const Loop loop = *state->loop;
	const Sample* sample = state->sample;
	int& index = state->frameIndex;
	bool& backwards = state->backwards;

loop is just an enum and sample is a pointer, so they don't need a const reference