Add regression test for escaping feature names

[AlexWheeler]

@jnunemaker great idea about adding a regression test lemme know what ya think

• 7151715 was merged which escapes
  feature_names like we were doing before the change to support slashes
  and adding the FeatureNameFromRoute module for pulling the feature name
  out of the request. This adds a regression spec to make sure this
  continues to work in the future as changes are made.

• I decided to test this in a separate describe block since the current action_subclass is super simple and really easy to understand what its testing. Since the FeatureNameFromRoute returns a request body with values and includes a module, etc I think its nice to separate the two. Since feature_name is a private method I didn't really want to test it using send and instead decided to run the fake request via the public run method like the other specs have. If you like this approach I'll add the same for Api::Action just lemme know. Totally open to other suggestions to better test this too

• I decided to stub path_info instead of add the header PATH_INFO to env because that feels like messing with internals of the path_info method and we just care about the public method and not how its implemented under the hood