Symbolize names and freeze values when loading from JSON

JSON.load_file being defined implies that symbolize_names and freeze
options are supported at parse time. We use this as a best effort
feature test.

lib/i18n/backend/base.rb

@@ -253,7 +253,12 @@ def load_yml(filename)
         # toplevel keys.
         def load_json(filename)
           begin
-            ::JSON.parse(File.read(filename))
+            # Use #load_file as a proxy for a version of JSON where symbolize_names and freeze are supported.
+            if JSON.respond_to?(:load_file)
+              ::JSON.load_file(filename, symbolize_names: true, freeze: true)
+            else
+              ::JSON.parse(File.read(filename))
+            end
           rescue TypeError, StandardError => e
             raise InvalidLocaleData.new(filename, e.inspect)
           end

test/backend/simple_test.rb

@@ -77,7 +77,11 @@ def setup
 
   test "simple load_json: loads data from a JSON file" do
     data = I18n.backend.send(:load_json, "#{locales_dir}/en.json")
-    assert_equal({ 'en' => { 'foo' => { 'bar' => 'baz' } } }, data)
+    assert_equal({ :en => { :foo => { :bar => 'baz' } } }, data)
+
+    if JSON.respond_to?(:load_file)
+      assert_predicate data.dig(:en, :foo, :bar), :frozen?
+    end
   end
 
   test "simple load_translations: loads data from known file formats" do