Replaces existingColumn with newColumn in this table.
Source
void replaceColumn(SchemaColumn existingColumn, SchemaColumn newColumn) {
existingColumn = this[existingColumn.name];
if (existingColumn == null) {
throw new SchemaException("Column ${existingColumn.name} does not exist on $name.");
}
var index = _columnStorage.indexOf(existingColumn);
_columnStorage[index] = newColumn;
newColumn.table = this;
existingColumn.table = null;
}