Gets rid of the largest set of mutable global state within the core.
This also paves a way for eliminating usages of GetInstance() on the
System class as a follow-up.
Note that no behavioral changes have been made, and this simply extracts
the functionality into a class. This also has the benefit of making
dependencies on the core timing functionality explicit within the
relevant interfaces.
Preserves the meaning/type-safetiness of the stream state instead of
making it an opaque u32. This makes it usable for other things outside
of the service HLE context.
Avoids including unnecessary headers within the audio_renderer.h header,
lessening the likelihood of needing to rebuild source files including
this header if they ever change.
Given std::vector allows forward declaring contained types, we can move
VoiceState to the cpp file and hide the implementation entirely.
GetAudioRendererSampleRate is set as a "STUB" as a game could check if the sample rate it sent and the sample rate it wants don't match. Just a thought of something which could happen so keeping it as stub for the mean time
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