Proposal: Tables should expose an encodeKey() view

[yonadaa]

As part of the Factories PR (#749), I need to generically pass around table keys as an array of bytes32. This is difficult because the logic for serialising keys is inlined in table contracts:

 /** Get the full data (using the specified store) */
  function get(...) internal view returns (StaticsData memory _table) {
    bytes32[] memory _primaryKeys = new bytes32[](7);
    _primaryKeys[0] = bytes32(uint256((k1)));
    _primaryKeys[1] = bytes32(uint256(uint32((k2))));
    _primaryKeys[2] = bytes32((k3));
    _primaryKeys[3] = bytes32(bytes20((k4)));
    _primaryKeys[4] = _boolToBytes32((k5));
    _primaryKeys[5] = bytes32(uint256(uint8(k6)));
    _primaryKeys[6] = bytes32(uint256(uint8(k7)));

    bytes memory _blob = _store.getRecord(_tableId, _primaryKeys, getSchema());
    return decode(_blob);
  }

Like the encode() method for data, this logic should be moved to a encodeKey() method like:

  function encodeKey(...) internal pure returns (bytes32[] memory) {
    bytes32[] memory _primaryKeys = new bytes32[](7);
    _primaryKeys[0] = bytes32(uint256((k1)));
    _primaryKeys[1] = bytes32(uint256(uint32((k2))));
    _primaryKeys[2] = bytes32((k3));
    _primaryKeys[3] = bytes32(bytes20((k4)));
    _primaryKeys[4] = _boolToBytes32((k5));
    _primaryKeys[5] = bytes32(uint256(uint8(k6)));
    _primaryKeys[6] = bytes32(uint256(uint8(k7)));

    return _primaryKeys;
  }

I experimentally added this functionality here but it should be moved to a separate PR.

[dk1a]

I agree, the rendering logic is already encapsulated in _primaryKeysDefinition, I haven't made a separate method only because it hasn't been needed yet