Rename pt to pt_PT in svn

[hanyoung]

Hello everyone,

I'd like to rename `pt` directory in our svn to `pt_PT` to fix the bug that most applications treat `pt` as `pt_BR`.
My understanding is that `l10n-kf5/$LANGUAGE/messages/plasma-workspace/plasmashell.po` will be sync to `plasma-workspace/po/$LANGUAGE/plasmashell.po`.
In turn, when we call `KLocalizedString::availableDomainTranslations("plasmashell").values()` in systemsetting to get the list of available languages,
it essentially iterates over the translation directories and return the list of directory names that have plasmashell.po in them.
And that's why we're getting ["pt", "pt_BR"]. Sadly, most applications (include KDE itself) treat `pt` as `pt_BR`. 
So effectively, user can't set their system language to `pt_PT` in systemsettings.

As a temporary measure, we can explicitly set 'pt' to 'pt_PT' in systemsettings code. As I did in this MR: https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/2478
However, I wish in the long term we can rename the 'pt' in https://websvn.kde.org/trunk/l10n-kf5/pt/ to 'pt_PT'. This should fix the root issue.

Relevant bug report, forum discussion and MR:
https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/2478
https://discuss.kde.org/t/rename-pt-in-i10n-svn-to-pt-pt/118
https://bugs.kde.org/show_bug.cgi?id=454991

Note: please reply on either MR, forum post or bug report. Forum post is preferred since I linked it to the MR and bug report (and also in source code comment)

Regards,
Han