[8.x] Add validation support for TeamSpeak3 URI scheme

[homotechsual]

This PR adds support for ts3server URI validation to the URL validator's list of protocols. Currently links to TeamSpeak3 servers fail validation as the ts3server protocol is not validated and the teamspeak protocol does not have support in most major browsers or the TeamSpeak3 application itself.

https://gaming.stackexchange.com/questions/51926/how-can-i-directly-link-to-a-teamspeak-server-on-my-website

[GrahamCampbell]

👎 for making any edits to this. We should keep it the same as Symfony's. You should instead PR this to Symfony.

[homotechsual]

👎 for making any edits to this. We should keep it the same as Symfony's. You should instead PR this to Symfony.

PRs have been accepted to change this list previously and Symfony's Validator component takes a quite different approach to protocol validation, the accepted protocols being passed to the URL constraint rather than maintaining a hardcoded central list in the code - I'm not sure there is a comparable upstream change to make to keep this in sync.

https://github.com/symfony/validator/blob/d05d14b7909a40c9c643bae833a5d11acf8212a1/Constraints/UrlValidator.php#L69
https://github.com/symfony/validator/blob/c466058e5ace12d439a2f68446f88f28d8e5a2b1/Constraints/Url.php#L32