[ticket/13859] Reorder static & public in migration
PHPBB3-13859

[ticket/13859] Allow up-to-date format for Youtube profile field URLs
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

[ticket/13859] Allow up-to-date format for Youtube profile field URLs
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

[ticket/13859] Reorder static & public in migration
PHPBB3-13859

[ticket/16981] Fix HTML-encoded emojis in email subject line
PHPBB3-16981

[ticket/16981] Fix HTML-encoded emojis in email subject line
PHPBB3-16981

[ticket/16977] Fix broken tests
PHPBB3-16977

[ticket/16977] Move HTML rendering logic to template
PHPBB3-16977

[ticket/16977] Fix cron-job img tag layout and accessibility
PHPBB3-16977

[ticket/16977] Fix broken tests
PHPBB3-16977

[ticket/16977] Fix cron-job img tag layout and accessibility
PHPBB3-16977

[ticket/16977] Move HTML rendering logic to template
PHPBB3-16977