Inline small helper functions.

Inline the SetTileState and ClearTile methods in Grid as well as the bit
fields methods of the t-table. These functions are called many times in
the Minimax method and only execute one line.
Improve the depth + always implementation.
Reduce the number of lazy masks per cell.

Only up to one lazy vertical mask is needed per cell, as the cell cannot
have any pieces above it. Also convert the GetTTableHash method to a
property.