FifoPlayer: Copy data with memcpy instead of one byte at a time

[leoetlino]

Copying with memcpy/std::copy is a lot faster than writing one byte at a time. And the behavior should be fully equivalent.

All FastWrite8 does is write a byte and increment the pointer:

dolphin/Source/Core/Core/HW/GPFifo.cpp

Lines 144 to 148 in 5513d5f

	void FastWrite8(const u8 value)
	{
	*PowerPC::ppcState.gather_pipe_ptr = value;
	PowerPC::ppcState.gather_pipe_ptr += sizeof(u8);
	}

Before: https://f.leolam.fr/out-rs3.svg

After: https://f.leolam.fr/out-rs3_v2.svg

[JMC47]

This makes fifologs recorded from Rogue Squadron 3 run "full speed" and also makes a lot of other fifologs run at a much higher potential framerate.