this parameter was previously used to send blocks with a different set of flags, immediately, to players. However, the flags have been demonstrated useless and the direct sending is pointless now since packets are buffered now per session, so we might as well take advantage of the batched block update sending.
This is a major change to the way block metadata is handled within the PM core. This separates variant metadata (which really ought to be part of the ID) from state metadata, and in a couple of cases flattens separate states of blocks together.
The result of this is that invalid variants can be much more easily detected, and additionally state handling is much cleaner since meta is only needed at the serialize layer instead of throughout the code.
