deprecating implicitly inferring spec type
Improve wording of deprecation message.
Fix controller example group specs to be less stub-happy.

The fact that they stub `controller_class` (which is
changed by the `controller` macro being tested) got
in the way of further changes I need to make and was
a bad idea to begin with.
Add deprecation warning for use of `described_class` in group where the `controller` macro was used.
Add changelog entries.
Merge pull request #1004 from rspec/deprecation_for_infer_spec_type

 Add deprecation to 2.99 to instruct users to use `infer_spec_type_from_file_location!` when upgrading