[tiktok] add support (#3061 #4177 #5646 #6878 #6708)

* Add TikTok photo support

#3061
#4177

* Address linting errors

* Fix more test failures

* Forgot to update category names in tests

* Looking into re issue

* Follow default yt-dlp output template

* Fix format string error on 3.5

* Support downloading videos and audio

Respond to comments
Improve archiving and file naming

* Forgot to update supportedsites.md

* Support user profiles

* Fix indentation

* Prevent matching with more than one TikTok extractor

* Fix TikTok regex

* Support TikTok profile avatars

* Fix supportedsites.md

* TikTok: Ignore no formats error

In my limited experience, this doesn't mean that gallery-dl can't download the photo post (but this could mean that you can't download the audio)

* Fix error reporting message

* TikTok: Support more URL formats

vt.tiktok.com
www.tiktok.com/t/

* TikTok: Only download avatar when extracting user profile

* TikTok: Document profile avatar limitation

* TikTok: Add support for www.tiktokv.com/share links

* Address Share -> Sharepost issue

* TikTok: Export post's creation date in JSON (ISO 8601)

* [tiktok] update

* [tiktok] update 'vmpost' handling

just perform a HEAD request and handle its response

* [tiktok] build URLs from post IDs

instead of reusing unchanged input URLs

* [tiktok] combine 'post' and 'sharepost' extractors

* [tiktok] update default filenames

put 'id' and 'num' first to ensure better file order

* [tiktok] improve ytdl usage

- speed up extraction by passing '"extract_flat": True'
- pass more user options and cookies
- pre-define 'TikTokUser' extractor usage

* [tiktok] Add _COOKIES entry to AUTH_MAP

* [tiktok] Always download user avatars

* [tiktok] Add more documentation to supportedsites.md

* [tiktok] Address review comments

---------

Co-authored-by: Mike Fährmann <mike_faehrmann@web.de>

docs/supportedsites.md

@@ -1,6 +1,7 @@
 # Supported Sites
 
 <!-- auto-generated by scripts/supportedsites.py -->
+
 Consider all listed sites to potentially be NSFW.
 
 <table>
@@ -937,6 +938,16 @@ Consider all listed sites to potentially be NSFW.
     <td>Galleries</td>
     <td></td>
 </tr>
+<tr>
+    <td>TikTok</td>
+    <td>https://www.tiktok.com/</td>
+    <td>Posts, User Profiles, VM Posts</td>
+    <td><a href="https://github.com/mikf/gallery-dl#cookies">Cookies</a>
+    <br /><span title="Pass `-o videos` to download photos only, and
+    `-o tiktok-range=a-yt-dlp-range` to tell yt-dlp to only extract XYZ links
+    when scraping a user profile. Also note that profile avatars will only be
+    downloaded when downloading a User Profile.">Hover for more info</span></td>
+</tr>
 <tr>
     <td>TMOHentai</td>
     <td>https://tmohentai.com/</td>