add new sanitizing prefs in advance of 136

[1888466](https://bugzilla.mozilla.org/show_bug.cgi?id=1888466) Unmerge "Browsing & Download History" and "Form & Search History" in the new Clear Data/History dialog
- [1944566](https://bugzilla.mozilla.org/show_bug.cgi?id=1944566) "search and form history" no longer auto-cleared on shutdown