Refactor the vectors mod

[evenyag]

Some Ideas about the vectors mod

logical type and physical type

We should allow the Vector has a logical type and a physical type

• vectors like DateVector, TimestampVector could benefit from this, as we could update the logical data type of the underlying PrimitiveVector and then delegate all methods to it
• NullVector could has a logical type of any data type, so we could easily create a null vector for other data types

[evenyag]

Another problem is that when downcasting the vector, the actually vector may be a constant vector and unable to be handled by the ScalarVector trait.

So to downcast the vector correctly, we may need to check the physical type of the vector (if constant is not a physical type, we also need to check whether the vector is const first)