[twitter] improve results for regular user URLs

- continuation of 3346f58a
- use media timeline results (or tweet timeline if retweets are enabled)
  plus search results starting from the last tweet id of the first
  timeline, similar to how Twitter Media Downloader operates
- the old behavior can be forced by appending '/tweets' to a user URL,
  like with '/media' (https://twitter.com/USER/tweets)
  although there should be no need to ever do that

docs/configuration.rst

@@ -2366,6 +2366,7 @@ Description
     Special values:
 
     * ``"timeline"``: ``https://twitter.com/i/user/{rest_id}``
+    * ``"tweets"``: ``https://twitter.com/id:{rest_id}/tweets``
     * ``"media"``: ``https://twitter.com/id:{rest_id}/media``
 
     Note: To allow gallery-dl to follow custom URL formats, set the blacklist__