Condition could have more detailed fields

Currently, when I parse a query, I get WHERE as Condition instances. These have an expr field, which is just a string and not very useful when analyzing a query. It would be really nice if we could be able to get more detail from that, like the operator, operands, etc.

Examples:

// c.id = 2
[
    leftOperand: ColumnReference [ column: 'id', tableAlias: 'c' ] ,
    operator: Equals []
    rightOperand: Constant [ value: 2 ]
]

// customer.address_id IS NOT NULL
[
    leftOperand: ColumnReference [ column: 'address_id', tableName: 'customer' ] ,
    operator: IsNotNull
    rightOperand: null
]

Comienza localizando las instancias de Condition del parser y el campo expr existente. Compara los ejemplos solicitados c.id = 2 y customer.address_id IS NOT NULL y, a continuación, define qué información estructurada sobre el operador y el operando debe exponerse; el trabajo estará terminado cuando las condiciones proporcionen ese detalle en lugar de solo una cadena.