Per the tracker issue:
> In 3.1 a youtube profilefield was added in which we can insert our youtube
> username to link to it.... There is just one major problem though...
>
> New youtube members no longer get an username. So I think we should decide on
> providing different ways to access their profile.
This PR will allow users to use any valid YouTube-domain URL, which allows for
all 3 formats (`/channel/...`, `/c/...`, and the now-legacy `/user/...`).
Per [YouTube's docs](https://support.google.com/youtube/answer/6180214?hl=en):
> ## Channel URL (ID-based)
> Example: youtube.com/channel/UCUZHFZ9jIKrLroW8LcyJEQQ
>
> This is the standard URL that YouTube channels use.
>
> ...
>
> ## Custom URL
> Example: youtube.com/c/YouTubeCreators
>
> A custom URL is a shorter, easy-to-remember URL that you can share with your
> audience.
>
> ...
>
> ## Legacy username URL
> Example: youtube.com/user/YouTube
>
> Depending on when your channel was created, it may have a username. Usernames
> are no longer required for channels today, but you can still use this URL to
> direct to your channel — even if your channel name has changed since you chose
> your username. Existing usernames can't be changed.
PHPBB3-13859
Some phpBB forum notification emails send URLs to the forum with redundant URL
parameters, notably a forum IDs with topic URLs.
To have shorter and cleaner URLs, those are hereby removed.
Signed-off-by: MichaIng <micha@dietpi.com>
PHPBB3-16959
The deferred purge will be used in the future instead. The cache flag in the
router only causes additional issues by trying to rebuild the routing
mid-request
PHPBB3-16956
When enabling an extension, it should be considered as not being enabled for
the entire request as if the "enabled" flag is switch during the request, the
extension will stay not loaded (same when disabling an extension).
Example when it can be an issue today : if the router is called for the first
time after enabling the extension and if the extension uses a custom route
loader (like phpbb/pages) then the router will fail because the custom route
will be found but the custom loader will not be loaded and available.
PHPBB3-16891
