Bug 41520: (Regression) Rearranging bookmarks / place items by drag & drop doesn't work anymore

This together with tor-browser!482 (merged) is the 12.0 backport of tor-browser!481 (merged), fixing tor-browser#41520 (closed) (part of tor-browser#41518).

1. Keep the !106 (merged) fix against text/plain and text/html fallback flavors escaping the filter
2. Limit the protection to actual links (i.e. anchor elements or other DOM elements which cause a text/x-moz-url data flavor to be added to the transferable object) as it was originally meant
3. Drop any attempt to guess "selected text containing URLs"
4. Explicitly exempt bookmarks
5. Allow as much as possible dragging links onto the Tor Browser's own UI, for navigation and bookmarking purposes