[pholder] add support (#2568 #9067)

* feat: extractor for pholder.com
    Closes #2568
* feat[pholder]: support gallery_id properly and tags
* doc[text.nameext_from_name]: minor typo in docstring

* remove '__init__' & 'request' methods and 'json' import
* use 'text.nameext_from_url' to ensure a 'filename' value
* fix 'imgur' links by disabling auto-Referer
* fix 'data["id"].partition()' call
    'partition' returns 3 elements
* use 'item["_source"]' data directly
* remove unused supportedsites overwrite
* catch all exceptions in '_thumb_resolution'
    fixes "KeyError: 'width'"
* use 'author' name for user folders

---------

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

test/results/pholder.py

@@ -0,0 +1,47 @@
+# -*- coding: utf-8 -*-
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+from gallery_dl.extractor import pholder
+
+
+__tests__ = (
+{
+    "#url"     : "https://pholder.com/r/lavaporn",
+    "#category": ("", "pholder", "subreddit"),
+    "#class"   : pholder.PholderSubredditExtractor,
+    "#range"   : "1-20",
+    "#count"   : ">= 20",
+},
+
+{
+    "#url"     : "https://pholder.com/r/lavaporn/",
+    "#category": ("", "pholder", "subreddit"),
+    "#class"   : pholder.PholderSubredditExtractor,
+},
+
+{
+    "#url"     : "https://pholder.com/u/automoderator",
+    "#category": ("", "pholder", "user"),
+    "#class"   : pholder.PholderUserExtractor,
+    "#range"   : "1-20",
+    "#count"   : ">= 20",
+},
+
+{
+    "#url"     : "https://pholder.com/u/automoderator/",
+    "#category": ("", "pholder", "user"),
+    "#class"   : pholder.PholderUserExtractor,
+},
+
+{
+    "#url"     : "https://pholder.com/search-text",
+    "#category": ("", "pholder", "search"),
+    "#class"   : pholder.PholderSearchExtractor,
+    "#range"   : "1-10",
+    "#count"   : "== 10",
+},
+
+)