DSP LLE: Rename CMPAR to CMPAXH

[Pokechu22]

The old name implies that it works on the address registers (like DAR/IAR/SUBARN/ADDARN), while the new name is consistent with TSTAXH and MULAXH. This PR also adds a test that covers CMPAXH and TSTAXH. This PR is intended to be merged before #10692.

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Note that CMPAR wasn't included in the manual until #10048 (specifically 211c2b5), but was described in some notes without giving it a name (on http://hitmen.c02.at/html/gc_tools.html for DSP Suite, look in the zip's gcdspsuite/doc/reverse.txt and reverse_new.txt):

0xc100 - 0xd100
|110r a001 ---- ----|
compare $acca with $(1a+r)
$acca < $(r1a)	28
$acca > $(r1a)	21
$acca = $(r1a)	25	// equal only if acc.1c == 0

In the initial megacommit, it existed in the table as CMPAXH and as cmpar in the actual implementation:

dolphin/Source/Plugins/Plugin_DSP_LLE/Src/gdsp_opcodes.cpp

Lines 551 to 563 in 775dc8a

	void dsp_opc_cmpar(uint16 opc)
	{
	uint8 rreg = ((opc >> 12) & 0x1) + 0x1a;
	uint8 areg = (opc >> 11) & 0x1;
	// we compare
	sint64 rr = (sint16)g_dsp.r[rreg];
	rr <<= 16;
	sint64 ar = dsp_get_long_acc(areg);
	Update_SR_Register(ar - rr);
	}

dolphin/Source/Plugins/Plugin_DSP_LLE/Src/opcodes.cpp

Line 146 in 775dc8a

{"CMPAXH", 0xc100, 0xe7ff, 1 | P_EXT, 2, {{P_ACCM, 1, 0, 12, 0x1000}, {P_REG1A, 1, 0, 11, 0x0800}},},

In 472e673 it was renamed to CMPAR in the table, but also commented out due to a separate bug. That bug was fixed in 8b6b8b6. There was an additional mistake that was fixed in 4747cc7.