Purpose: Add "Share..." context menu entry to "tabs" context
Just like KDE Connect devices makes the "Share..." available on the tab bar in Firefox.
Got a "Share…" menu in my tab bar for kde.org but not for about:tabs
Adding a restriction to the generic menu needs a split between documenturlpatterns/targeturlpatterns/nothing for selection, etc, which is outside the scope of this patch. I just wanted to avoid the "Share…" needlessly showing up on all the tabs.