QAudioSource/QAudioSink have a private interface for callback-based API. we want to expose this to a public API.

Details:

Currently, we work with audio data through QIODevice, and the current use case is supposed to be used from the user thread.
Advanced users often need to be able to access the underlying audio thread through a callback, so we're providing a new api for running QAudioSink/QAudioSource with a callback.
We want to have the API type-safe: run a callback for the data type relevant to the underlying sample format. It means that for covering current formats, the callback should be a callable object with one of the signatures (might be extended later on).

void(QSpan<int8_t>), void(QSpan<uint16_t>), void(QSpan<uint32_t>), void(QSpan<float>)