Bug 1950056 - extend use of FOS_NODEREFERENCELINKS r=Gijs,win-reviewers,gstoll

In the modern era of user-customizable Quick Access sidebars on every
file dialog, navigating via `.lnk` files is rather less useful than it
was twenty years ago.

Disable link-following in file-open dialogs by default, to prevent any
of the usual security issues involving symlink smuggling. Allow
overriding this behavior via a pref, for users who don't care.

(File-save dialogs have a more nuanced guard against that sort of thing;
this patch doesn't affect that.)

Differential Revision: https://phabricator.services.mozilla.com/D239833