Numericality validations for aliased attributes are not able
to get the value of the attribute before type cast because
activerecord was trying to get the value of the attribute based
on attribute alias name and not the original attribute name.

Example of validation which would pass even if a invalid value
would be provided

    class MyModel < ActiveRecord::Base
      validates :aliased_balance, numericality: { greater_than_or_equal_to: 0 }
    end

If we instantiate MyModel like bellow it will be valid because
when numericality validation runs it will not be able to get the
value before type cast, so it uses the type casted value
which will be `0.0` and the validation will match.

    subject = MyModel.new(aliased_balance: "abcd")
    subject.valid?

But if we declare MyModel like this

    class MyModel < ActiveRecord::Base
      validates :balance, numericality: { greater_than_or_equal_to: 0 }
    end

and assign "abcd" value to `balance` when the validations
run the model will be invalid because activerecord will be able
to get the value before type cast.

With this change `read_attribute_before_type_cast` will be able to
get the value before type cast even when the attr_name is an
attribute_alias.