Add back Variant#find_or_build_default_price

This method was renamed to `default_price_or_build` with 6420b10, but
this was a breaking change given it was released with Solidus 3.1.
This commit reintroduces the method as an alias but with deprecation.

core/app/models/concerns/spree/default_price.rb

@@ -32,6 +32,11 @@ def default_price_or_build
         prices.build(self.class.default_price_attributes)
     end
 
+    def find_or_build_default_price
+      default_price_or_build
+    end
+    deprecate :find_or_build_default_price, deprecator: Spree::Deprecation
+
     # Select from {#prices} the one to be considered as the default
     #
     # This method works with the in-memory association, so non-persisted prices

core/spec/models/spree/variant_spec.rb

@@ -334,6 +334,21 @@
     end
   end
 
+  describe '#find_or_build_default_price' do
+    it 'is deprecated' do
+      without_partial_double_verification do
+        expect(Spree::Deprecation).to receive(:warn)
+      end
+      variant.find_or_build_default_price
+    end
+
+    it 'is an alias for #default_price_or_build' do
+      expect(variant).to receive(:default_price_or_build)
+
+      variant.find_or_build_default_price
+    end
+  end
+
   describe '#has_default_price?' do
     context 'when default price is present and not discarded' do
       it 'returns true' do