core_timing: Convert core timing into a class

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.

src/audio_core/audio_renderer.h

@@ -14,6 +14,10 @@
 #include "common/swap.h"
 #include "core/hle/kernel/object.h"
 
+namespace Core::Timing {
+class CoreTiming;
+}
+
 namespace Kernel {
 class WritableEvent;
 }
@@ -208,7 +212,7 @@ static_assert(sizeof(UpdateDataHeader) == 0x40, "UpdateDataHeader has wrong size
 
 class AudioRenderer {
 public:
-    AudioRenderer(AudioRendererParameter params,
+    AudioRenderer(Core::Timing::CoreTiming& core_timing, AudioRendererParameter params,
                   Kernel::SharedPtr<Kernel::WritableEvent> buffer_event);
     ~AudioRenderer();