Shader: lower VOP3P V_FMA_MIX_F32/LO/HI (was dropping Unity HDR shaders) (#466)

The decoder recognises the VOP3P mix ops (0x20 V_FMA_MIX_F32, 0x21
V_FMA_MIXLO_F16, 0x22 V_FMA_MIXHI_F16) but left them opaque
(Vop3pRaw20/21/22), so at SPIR-V emission they fell through the
vector-ALU switch to the default and failed with "unsupported vector
opcode". A single unhandled instruction fails the whole compile, so any
shader using fma_mix was dropped entirely. Unity's built-in-RP /
PostProcessing v2 HDR, tone-mapping and auto-exposure shaders emit
V_FMA_MIX_F32, so those passes never translated (this is what kept
Superliminal's auto-exposure luminance chain from running).

Name the three opcodes in DecodeVop3p (like the packed v_pk_* ops) and
lower them in the SPIR-V translator. Each mix op computes a single f32
fma(a, b, c) where every source is read *independently* as either a full
f32 register/constant or one f16 half widened to f32. Per operand,
op_sel_hi selects f16-vs-f32 and op_sel picks which f16 half; the neg_hi
field is repurposed as an absolute-value modifier and neg negates,
applied abs-then-neg. This reuses the VOP3P op_sel/op_sel_hi/neg/neg_hi
bit layout with the mix-specific meaning, not the packed-math meaning.
The result is a scalar f32 for V_FMA_MIX_F32; _MIXLO/_MIXHI narrow it
back to f16 (exact round-to-nearest-even, via the existing
EmitFloatToHalf) and write it into the low/high 16 bits of vdst,
preserving the other half. The clamp modifier saturates to [0, 1]
consistently with the other VOP3P ops. Per-operand F16/F32 select and
the abs/neg modifiers follow shadPS4's GetSrcMix, the authoritative
reference for the mix semantics.

Adds Gen5FmaMixSpirvTests: assembles V_FMA_MIX_F32 (with a representative
op_sel/op_sel_hi/neg/abs) and V_FMA_MIXLO_F16 compute shaders and asserts
they translate to GPU SPIR-V without hitting the drop path and emit a
GLSL.std.450 Fma (and an FAbs for the neg_hi modifier). Both fail against
the pre-fix tree with "unsupported vector opcode Vop3pRaw20/21".

src/SharpEmu.ShaderCompiler/Gen5ShaderTranslator.cs

@@ -1192,8 +1192,10 @@ public static class Gen5ShaderTranslator
 
         // Opcode numbers taken from LLVM's AMDGPU VOP3PInstructions.td and the
         // gfx9/gfx10 MC test encodings; they are unchanged across gfx9 and gfx10.
-        // Unhandled packed opcodes (integer, fma_mix, ...) stay opaque here and
-        // fail loudly at emission rather than being silently mis-emitted.
+        // The mix ops (0x20/0x21/0x22) are V_MAD_MIX_* on gfx9 and V_FMA_MIX_*
+        // (fused) on the gfx10 the PS5 targets; both share these opcodes. Any
+        // remaining packed opcode (integer, ...) stays opaque here and fails
+        // loudly at emission rather than being silently mis-emitted.
         name = opcode switch
         {
             0x0E => "VPkFmaF16",
@@ -1201,6 +1203,9 @@ public static class Gen5ShaderTranslator
             0x10 => "VPkMulF16",
             0x11 => "VPkMinF16",
             0x12 => "VPkMaxF16",
+            0x20 => "VFmaMixF32",
+            0x21 => "VFmaMixloF16",
+            0x22 => "VFmaMixhiF16",
             _ => $"Vop3pRaw{opcode:X2}",
         };