Core/DSPHLE: Move AESndAccelerator instance into AESndUCode.

[AdmiralCurtiss]

This changes the AESndAccelerator instance from global state to state local to each AESndUCode instance. I'm not sure whether this has side-effects (is this state intendend to persist across unload and reload of an UCode?), so this may need a different approach if it does.

Untested.

[Pokechu22]

Can confirm that the modplay.elf homebrew example (which uses aesnd) works properly with this change.

is this state intendend to persist across unload and reload of an UCode

It probably works that way in practice on real hardware (unless aesnd happens to fully reinitialize it in all cases), but this wasn't something I was trying to model. I just implemented it that way because I was copying what was done in AXVoice.h:

dolphin/Source/Core/Core/HW/DSPHLE/UCodes/AXVoice.h

Line 200 in 8a9d168

static std::unique_ptr<Accelerator> s_accelerator = std::make_unique<HLEAccelerator>();

(which I see you've changed in #12487).