vertexcodec: Update kBitsV1 table for slightly better compression

This table was found by bruteforcing all 455 permutations of 15 possible
bit combinations in each entry; the best result was ~4.90% reduction,
but for now we pick the version with 0/2/4/8 as one of the entries
(which is ~4.83% reduction) as that makes it easier to retain
compatibility with v0. The previous table that this code replaces got
~4.59% reduction.

The new table also makes more logical sense: 0/1/2/4 optimizes for
well-compressible data, and 1/4/6/8 optimizes for poorly-compressible
data. 2/4/6/8 would perhaps make more sense, but 1/4/6/8 performs
better.

src/vertexcodec.cpp

@@ -124,8 +124,8 @@ const size_t kTailMaxSize = 32;
 static const int kBitsV0[4] = {0, 2, 4, 8};
 static const int kBitsV1[3][4] = {
     {0, 2, 4, 8},
-    {0, 1, 2, 8},
-    {2, 4, 6, 8},
+    {0, 1, 2, 4},
+    {1, 4, 6, 8},
 };
 
 static size_t getVertexBlockSize(size_t vertex_size)