PanasonicV8Decompressor: use proper builtin for bitreverse (-31%)

```
Comparing /home/lebedevri/rawspeed/build-old/src/utilities/rsbench/rsbench to /home/lebedevri/rawspeed/build-new/src/utilities/rsbench/rsbench
Benchmark                                                                          Time             CPU      Time Old      Time New       CPU Old       CPU New
---------------------------------------------------------------------------------------------------------------------------------------------------------------
P1126458_mechanical.RW2/threads:1/process_time/real_time_pvalue                  0.0000          0.0000      U Test, Repetitions: 99 vs 99
P1126458_mechanical.RW2/threads:1/process_time/real_time_mean                   -0.2704         -0.2703           208           152           208           152
P1126458_mechanical.RW2/threads:1/process_time/real_time_median                 -0.2710         -0.2711           208           151           208           151
P1126458_mechanical.RW2/threads:1/process_time/real_time_stddev                 +1.1693         +3.3262             0             0             0             0
P1126458_mechanical.RW2/threads:1/process_time/real_time_cv                     +1.9731         +4.9285             0             0             0             0
P1126458_mechanical.RW2/threads:32/process_time/real_time_pvalue                 0.0000          0.0000      U Test, Repetitions: 99 vs 99
P1126458_mechanical.RW2/threads:32/process_time/real_time_mean                  -0.3076         -0.3077           112            78           224           155
P1126458_mechanical.RW2/threads:32/process_time/real_time_median                -0.3076         -0.3077           112            78           224           155
P1126458_mechanical.RW2/threads:32/process_time/real_time_stddev                -0.1431         -0.2072             0             0             0             0
P1126458_mechanical.RW2/threads:32/process_time/real_time_cv                    +0.2376         +0.1451             0             0             0             0
OVERALL_GEOMEAN                                                                 -0.2892         -0.2892             0             0             0             0

```

Author: LebedevRI

src/librawspeed/adt/Bit.h

@@ -134,4 +134,16 @@ constexpr typename std::make_signed_t<T>
   return static_cast<SignedT>(value << SpareSignBits) >> SpareSignBits;
 }
 
+template <class T>
+  requires std::same_as<T, uint8_t>
+T bitreverse(const T v) {
+#if __has_builtin(__builtin_bitreverse8)
+  return __builtin_bitreverse8(v);
+#endif
+  // Reverse the order of bits within each byte using a bit-twiddle trick.
+  // Three operation bit reversal from:
+  // https://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith64BitsDiv
+  return uint8_t((uint8_t(v) * 0x0202020202ULL & 0x010884422010ULL) % 1023);
+}
+
 } // namespace rawspeed

src/librawspeed/decompressors/PanasonicV8Decompressor.cpp

@@ -89,13 +89,8 @@ struct BitStreamerReversedSequentialReplenisher
       std::copy_n(currInput.begin(), BitStreamerTraits<Tag>::MaxProcessBytes,
                   tmp.begin());
 
-      // Reverse the order of bits within each byte using a bit-twiddle trick.
-      // Three operation bit reversal from:
-      // https://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith64BitsDiv
-      for (std::byte& b : tmp) {
-        b = std::byte{
-            uint8_t((uint8_t(b) * 0x0202020202ULL & 0x010884422010ULL) % 1023)};
-      }
+      for (std::byte& b : tmp)
+        b = std::byte{bitreverse(uint8_t(b))};
 
       return tmpStorage;
     }