Fix Dimension::splitting_value for signed and negative inputs (#1725)
Fix Dimension::splitting_value for signed and negative inputs (#1725)

The bitwise calculation for the partitioner's dimension splitting value uses
an extra high to avoid overflow mid-calculation. The types may be signed or
unsigned. If the input arguments are signed and negative, we need to flip the
high bit to maintain two's complement notation.

Co-authored-by: Joe Maley <16a9a54ddf4259952e3c118c763138e83693d7fd@tiledb.com>
TileDB-Inc/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB