[AGC] Correct VReadlaneB32 decode and emission (#237)

VReadlaneB32 (VOP3 0x360) had two bugs:

1. Decode: VOP3 decode always set destinations = Vector(word & 0xFF).
   For VReadlaneB32, bits 0-7 are unused — the scalar destination is
   in bits 8-14. Now decodes as Scalar((word >> 8) & 0x7F).

2. Emission: VReadlaneB32 was in the VMovB32 fall-through group,
   just returning GetRawSource(instruction, 0) — reading the current
   lane's value. By ISA, sdst = vsrc0[lane(src1)], which requires
   reading a different lane's value. Now uses SPIR-V
   GroupNonUniformBroadcast(scope=Subgroup, value=src0, lane=src1)
   when subgroup operations are available, with a fallback to the
   current-lane simplification when not.

3. Routing: TryEmitVectorAlu called TryGetVectorDestination first,
   which checks for VectorRegister kind. With the scalar destination
   fix, VReadlaneB32 now routes to a new TryEmitReadlane handler
   before the vector destination check.

4. Subgroup capability: UsesSubgroupShuffle now includes VReadlaneB32
   so GroupNonUniform capability is enabled when needed.

Verified: dotnet build 0 errors/0 warnings, 26/26 tests pass,
ShaderDump all programs behaved as expected.

src/SharpEmu.ShaderCompiler.Vulkan/Gen5SpirvTranslator.cs

@@ -2507,7 +2507,7 @@ public static partial class Gen5SpirvTranslator
 
         private bool UsesSubgroupShuffle() =>
             _state.Program.Instructions.Any(instruction =>
-                instruction.Opcode is "VPermlane16B32" or "VPermlanex16B32");
+                instruction.Opcode is "VPermlane16B32" or "VPermlanex16B32" or "VReadlaneB32");
 
         private bool UsesWaveControl() =>
             _state.Program.Instructions.Any(instruction =>