Refactor social sharing helper

[tomhughes]

This implements the refactorings suggested in #5415 and also improves the testing of the generated HTML to ensure that all the buttons are generated and reference the correct URL and title.

[AntonKhorev]

Are you sure you escape things correctly?

[kcne]

Everything works well on my side. Thank you.

[kcne]

Are you sure you escape things correctly?

This only happens on Mastodon Share links. Must be something related to their implementation. I'm not sure if the code is opensource since i could not find the github repo. On the web site about page there is only this information:

MastodonShare is 100% private, 100% free, and 100% secure. It does not store or track anything about the visitors, usernames, instances, links or content. It does not require Mastodon API access.

If you have any questions, please ask me [email protected] or @[email protected].

[AntonKhorev]

Looks like & gets unescaped in mastodonshare.com's redirect location.

Request headers:

GET /?text=A%26B&url=http%3A%2F%2F127.0.0.1%3A3000%2Fuser%2Ffakeuser1%2Fdiary%2F86 HTTP/1.1
Host: mastodonshare.com
...

Response headers:

HTTP/1.1 302 Found
...
Location: https://en.osm.town/share?text=A&B%0A%0Ahttp://127.0.0.1:3000/user/fakeuser1/diary/86

Then it's not related to this pull request, same happens in the already deployed version.

[gravitystorm]

Thanks for the refactoring!