optimize supports_feature_mixin helper

This ensures unsupported_reason is stubbed for both supports and non-supports cases
(the number of calls to supports is reducing)

Since supports? and #unsupported_reason is just a minor shim over .unsupported_reason,
left those methods as is. Only stubbing .unsupported_reason

This also removes the allow_any_instance_of

spec/support/supports_helper.rb

@@ -4,31 +4,24 @@ module SupportsHelper
       # when testing a model that receives multiple supports,
       # put this down first to allow the other supports to work fine.
       def stub_supports_all_others(model)
-        allow_any_instance_of(model).to receive(:supports?).and_call_original
+        allow(model).to receive(:unsupported_reason).and_call_original
       end
 
       # when testing requests, ensure the model supports a certain attribute
-      def stub_supports(model, feature = :update, supported: true)
+      def stub_supports(model, feature = :update, supported: true, reason: nil)
         model = model.class unless model.kind_of?(Class)
         feature = feature.to_sym
 
-        receive_supports = receive(:supports?).with(feature).and_return(supported)
-        allow(model).to receive_supports
-        allow_any_instance_of(model).to receive_supports
+        reason = supported ? nil : (reason || SupportsFeatureMixin.default_supports_reason)
+        allow(model).to receive(:unsupported_reason).with(feature, :instance => anything).and_return(reason)
 
-        allow(model).to receive(:types_supporting).with(feature).and_return([nil] + model.descendants.map(&:name))
+        if supported
+          allow(model).to receive(:types_supporting).with(feature).and_return([nil] + model.descendants.map(&:name))
+        end
       end
 
       def stub_supports_not(model, feature = :update, reason = nil)
-        model = model.class unless model.kind_of?(Class)
-        feature = feature.to_sym
-
-        stub_supports(model, feature, :supported => false)
-
-        reason ||= SupportsFeatureMixin.default_supports_reason
-        receive_reason = receive(:unsupported_reason).with(feature).and_return(reason)
-        allow(model).to(receive_reason)
-        allow_any_instance_of(model).to(receive_reason)
+        stub_supports(model, feature, :supported => false, :reason => reason)
       end
     end
   end