File: get show hidden files from gsettings

[danirabbit]

get settings directly from gsettings instead of an intermediary object

[jeremypw]

Even though ensure_sizer () is called repeatedly during loading of files, I did see of significant change in loading time for folders containing 5000 items so presumably the Settings backend caches the setting anyway.

[jeremypw]

The CI passed locally, but failed on GitHub because the schema is not installed.

[danirabbit]

Hm I'm not sure how to resolve this. I'll revisit with more coffee maybe. At least this exposes a problem with FilesPreferences being in core but the actual gsettings being set elsewhere 😅

[jeremypw]

@danirabbit I proposed one way of working around the CI problem but not sure its acceptable. As there are only a couple of places where the app_settings are used in Files I have allowed for the settings to be null (not found in the default schemasource). There may be a better way to search elsewhere under test conditions. The settings are not actually used in test as they relate to the view appearance.