Unify linkify usage, move to linkify-string

[raimund-schluessler]

This unifies the linkify-string usage (we had this function in two places) and switches to the linkify-string package which replaces linkifyjs/string since the latest major release of linkifyjs.

Supersedes #2257.

Closes #1488.

[nickvergessen]

Ref #1678

We have to check if Safari still works with this

[raimund-schluessler]

Ref #1678

We have to check if Safari still works with this

At least for Safari on iOS it still works properly.

Also see nextcloud/calendar#3490 where the changes are present already.

The previously used linkifyjs/string just moved to its own package linkify-string. So it's the same Code that is used, just without the rest of linkify. This might even reduce the bundle size (need to check).

[raimund-schluessler]

I checked the bundle size, and it stays quite exactly the same. Webpack only bundled linkifyjs/string before and now only bundles linkify-string and both are the same size (and don't include jquery). So, #1488 shouldn't be an issue anyway anymore.

I fixed a small issue with linkification in the AppSidebar title, because now the server a.external style applies, which introduced a left/right margin for links. I overwrote this to not change the AppSidebar style.

I think this PR should be good now (maybe just test, that it really works with Safari on the Desktop).

[st3iny]

Looks good. I left some minor remarks regarding the documentation.

delivered

[st3iny]

LGTM! Please squash before merging :)

[raimund-schluessler]

/backport to stable4