title: Check if ISO 8601 string is in UTC
body: <p>I want a TypeScript function that checks if an ISO 8601 datetime string is in UTC. So the output should be:</p>
  <pre class="lang-js prettyprint-override"><code>isUTC('2020-01-01T00:00:00Z')      // true
  isUTC('2020-01-01T00:00:00+00')    // true
  isUTC('2020-01-01T00:00:00+0000)   // true
  isUTC('2020-01-01T00:00:00+00:00') // true
  isUTC('2020-01-01T00:00:00+01)     // false
  isUTC('2020-01-01T00:00:00+0100)   // false
  isUTC('2020-01-01T00:00:00+01:00') // false
  </code></pre>
  <p>If possible I would like to avoid regular expressions and use an existing parser or decomposer instead. Ideally there would be a library that decomposes ISO 8601 strings, so that I can check <code>Iso8601Decomposer(value).timezoneOffset === 0</code>. Does something like this exist in TypeScript/JavaScript?</p>
  <p>I found <a href="https://stackoverflow.com/questions/52869695/check-if-a-date-string-is-in-iso-and-utc-format">some answers</a> that were checking if <code>value === new Date(Date.parse(value)).toISOString()</code>, but this does not work for lines 2 and 3 above.</p>