[refactor] Move ComputeBlockVersion into VersionBitsCache

This also changes ComputeBlockVersion to take the versionbits cache
mutex once, rather than once for each versionbits deployment.

src/validation.cpp

@@ -1627,7 +1627,7 @@ public:
         return pindex->nHeight >= params.MinBIP9WarningHeight &&
                ((pindex->nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) &&
                ((pindex->nVersion >> bit) & 1) != 0 &&
-               ((ComputeBlockVersion(pindex->pprev, params) >> bit) & 1) == 0;
+               ((g_versionbitscache.ComputeBlockVersion(pindex->pprev, params) >> bit) & 1) == 0;
     }
 };