tests: cover low-alpha packed tiler conversion in both directions

tests/ShaderRecompilerComputeTests.cpp

@@ -20889,6 +20889,14 @@ public:
               std::swap(channels[0], channels[2]);
               std::memcpy(dst->data() + dst_offset, channels.data(),
                           sizeof(channels));
+            } else if (info.GetColorTransform() == ColorTransform::Rotate2_10_10_10) {
+              uint32_t packed = 0;
+              std::memcpy(&packed, src.data() + src_offset, sizeof(packed));
+              // The guest format stores the two-bit channel low; the host format stores it high.
+              const uint32_t alpha = to_tiled ? packed >> 30u : packed & 3u;
+              const uint32_t color = to_tiled ? packed & 0x3fffffffu : packed >> 2u;
+              packed = to_tiled ? (color << 2u) | alpha : color | (alpha << 30u);
+              std::memcpy(dst->data() + dst_offset, &packed, sizeof(packed));
             } else {
               std::memcpy(dst->data() + dst_offset, src.data() + src_offset,
                           block.bytes_per_element);
@@ -21282,6 +21290,8 @@ public:
         convert_reference(false, &cpu, tiled, layout);
         gpu_detile(tiled, &gpu, total.size, total.size, layout);
         compare("format bytes", cpu, gpu);
+        if (layout.GetColorTransform() == ColorTransform::Rotate2_10_10_10)
+          check_round_trip("low-alpha packed format", total.size, layout);
         ++format_cases;
       }
     }