title: Oracle timestamp cast with local time zone has different results in / out DST date range
body: <p>While checking timestamp transformation i'm stumbling over different timezone conversion in or out DST range.<br> 
  Knows Oracle the range from end of march to end of october? <br> 
  Are these results correctly?</p>
  
  <hr>
  
  <pre><code>SELECT DBTIMEZONE FROM dual;
  +02:00
  
  SELECT 
  TO_CHAR(CAST(TO_TIMESTAMP_TZ('2018-02-25T22:22:22+01:00','YYYY-MM-DD"T"HH24:MI:SS TZR') as timestamp with local time zone)), 
  TO_CHAR(CAST(TO_TIMESTAMP_TZ('2020-04-28T20:20:20+01:00','YYYY-MM-DD"T"HH24:MI:SS TZR') as timestamp with local time zone)) 
  FROM DUAL;
  
  OUTSIDE_DST                 INSIDE_DST
  25.02.18 22:22:22,000000    28.04.20 21:20:20,000000
  </code></pre>