incompeteFallbackMessage is not correct structure when building translations

[straker]

When we generate lang files using grunt translation --lang=<lang-code>, the incompleteFallbackMessage is generated as an object structure with undefined as a property name. However, the message in axe is always treated as just a string.

First, we need to fix the translation generator to output a string value instead of an object

incompleteFallbackMessage: result.misc.reduce(function(out, misc) {
  return misc.incompleteFallbackMessage ? misc.incompleteFallbackMessage : out
}, '')

Second, we need to update all the locale files to match the new format

// ja.json
"incompleteFallbackMessage": "次のすべてを修正します:{{~it:value}}\n  {{=value.split('\\n').join('\\n  ')}}{{~}}"

Third, we need to update the code that uses these translations to accept the new format

if (locale.incompleteFallbackMessage) {
  this.data.incompleteFallbackMessage = mergeFallbackMessage(
    this.data.incompleteFallbackMessage,
    locale.incompleteFallbackMessage
  );
}

Lastly, we need to update the associated test to show that it's all working

axe.configure({
  locale: {
    lang: 'lol',
    failureSummaries: {
      any: {
        failureMessage: 'foo'
      },
      none: {
        failureMessage: 'bar'
      }
    },
    incompleteFallbackMessage:  'baz'
  }
});

[jeankaplansky]

No customer-facing documentation required.

[padmavemulapati]

Verified , working as expected.
Seeing the japanese language failure summary, on running axe.ja.js (which is generating from grunt build --lang=ja)

"failureSummary": "次のすべてを修正します:\n  The lang attribute can only be Dylan"