glasm: Implement PrimitiveId attribute read

src/shader_recompiler/backend/glasm/emit_glasm_context_get_set.cpp

@@ -70,6 +70,9 @@ void EmitGetAttribute(EmitContext& ctx, IR::Inst& inst, IR::Attribute attr, Scal
         return;
     }
     switch (attr) {
+    case IR::Attribute::PrimitiveId:
+        ctx.Add("MOV.S {}.x,primitive.id;", inst);
+        break;
     case IR::Attribute::PositionX:
     case IR::Attribute::PositionY:
     case IR::Attribute::PositionZ: