Rails `DateTime` type is mapped to Oracle `TIMESTAMP` since Rails 5.0
Rails `DateTime` type is mapped to Oracle `TIMESTAMP` since Rails 5.0

Kind of reverting https://github.com/rails/rails/commit/3a1cbc5c3b3bcb2de4be6e4469bb87b99759dc59

```
From: test/cases/date_test.rb @ line 26 :

    21:
    22:     invalid_dates = [[2007, 11, 31], [1993, 2, 29], [2007, 2, 29]]
    23:
    24:     valid_dates.each do |date_src|
    25:       topic = Topic.new("last_read(1i)" => date_src[0].to_s, "last_read(2i)" => date_src[1].to_s, "last_read(3i)" => date_src[2].to_s)
 => 26:       binding.irb
    27:       assert_equal(topic.last_read, Date.new(*date_src))
    28:     end
    29:
    30:     invalid_dates.each do |date_src|
    31:       assert_nothing_raised do

irb(#<DateTest:0x0000556618194668>):001:0> topic.last_read.class
=> Date
```

Refer rsim/oracle-enhanced#845
rails/rails#25897

rafaelfranca/omg-rails,georgeclaghorn/rails,Edouard-chin/rails,repinel/rails,kddeisz/rails,fabianoleittes/rails,flanger001/rails,arunagw/rails,mechanicles/rails,MSP-Greg/rails,shioyama/rails,palkan/rails,Erol/rails,mechanicles/rails,Vasfed/rails,bogdanvlviv/rails,BlakeWilliams/rails,lcreid/rails,iainbeeston/rails,mechanicles/rails,Vasfed/rails,yhirano55/rails,kddeisz/rails,vipulnsward/rails,esparta/rails,kmcphillips/rails,esparta/rails,EmmaB/rails-1,MSP-Greg/rails,yahonda/rails,joonyou/rails,lcreid/rails,Vasfed/rails,EmmaB/rails-1,gauravtiwari/rails,Envek/rails,eileencodes/rails,shioyama/rails,eileencodes/rails,rafaelfranca/omg-rails,gauravtiwari/rails,notapatch/rails,joonyou/rails,joonyou/rails,betesh/rails,jeremy/rails,Stellenticket/rails,Edouard-chin/rails,rails/rails,fabianoleittes/rails,tjschuck/rails,notapatch/rails,yahonda/rails,tgxworld/rails,yawboakye/rails,EmmaB/rails-1,rails/rails,rails/rails,schuetzm/rails,yalab/rails,BlakeWilliams/rails,tjschuck/rails,georgeclaghorn/rails,BlakeWilliams/rails,repinel/rails,mechanicles/rails,vipulnsward/rails,Erol/rails,vipulnsward/rails,Stellenticket/rails,palkan/rails,kddeisz/rails,jeremy/rails,eileencodes/rails,schuetzm/rails,prathamesh-sonpatki/rails,kmcphillips/rails,joonyou/rails,Stellenticket/rails,yhirano55/rails,tgxworld/rails,schuetzm/rails,iainbeeston/rails,jeremy/rails,betesh/rails,gauravtiwari/rails,flanger001/rails,rafaelfranca/omg-rails,Envek/rails,tjschuck/rails,georgeclaghorn/rails,betesh/rails,lcreid/rails,yalab/rails,yhirano55/rails,Vasfed/rails,esparta/rails,kmcphillips/rails,georgeclaghorn/rails,yawboakye/rails,yalab/rails,fabianoleittes/rails,schuetzm/rails,repinel/rails,lcreid/rails,yawboakye/rails,yhirano55/rails,Envek/rails,flanger001/rails,tjschuck/rails,Stellenticket/rails,yahonda/rails,flanger001/rails,Edouard-chin/rails,jeremy/rails,shioyama/rails,yawboakye/rails,palkan/rails,iainbeeston/rails,notapatch/rails,palkan/rails,Erol/rails,fabianoleittes/rails,arunagw/rails,bogdanvlviv/rails,starknx/rails,vipulnsward/rails,yahonda/rails,prathamesh-sonpatki/rails,tgxworld/rails,arunagw/rails,rails/rails,eileencodes/rails,shioyama/rails,starknx/rails,yalab/rails,MSP-Greg/rails,notapatch/rails,tgxworld/rails,repinel/rails,bogdanvlviv/rails,Envek/rails,Erol/rails,kmcphillips/rails,starknx/rails,prathamesh-sonpatki/rails,iainbeeston/rails,prathamesh-sonpatki/rails,BlakeWilliams/rails,MSP-Greg/rails,esparta/rails,Edouard-chin/rails,kddeisz/rails,bogdanvlviv/rails,betesh/rails,arunagw/rails