Cache GKeyfileSettingsBackend to lower inotify usage
I got to a point where launching epiphany with my tab history consumes thousands of inotify handles (3.33.4 fwiw). This gets to starve all other processes for my user, with varying degrees of consequence.
I traced the bulk of them to the usage of GKeyfileSettingsBackend, each of them creates 2 monitors, and ephy creates one per GSettings requested on permissions.ini and web-extension-settings.ini, and there's quite a number of those created here.
Caching the settings backends for those ini files should keep inotify handle usage quite lower.
I'll eventually come up with a MR if no one beats me to it.