delete duplicated tests in AR base_test.rb

These are duplicated with the tests which are in relations_test.rb
Raise an error when query methods have blank arguments, and when blank arguments are meaningless.
Merge pull request #9258 from wangjohn/blank_argument_errors_in_arel

Raising an error when query methods have blank arguments.
small tweaks in the AR CHANGELOG
moves a CHANGELOG entry from AR to AP
Merge pull request #9315 from Takehiro-Adachi/remove-unecessary-tests-from-ar-base_testrb

delete duplicated tests in AR base_test.rb
fixes a typo in the migrations guide
s/revertible/reversible/
added more accurate test for add_on_empty

with the current tests, if delete the assignment of is_empty in add_on_empty method
the tests not fail. With this test, if we delete is_empty, the test fails
Merge pull request #9324 from acapilleri/add_on_empty

added more accurate test for add_on_empty