Adds setters and property delegates in `Settings` (#4809)

app/src/main/java/org/mozilla/fenix/BrowsingModeManager.kt

app/src/main/java/org/mozilla/fenix/FenixApplication.kt

...n/java/org/mozilla/fenix/components/BackgroundServices.kt

...ders/onboarding/OnboardingTrackingProtectionViewHolder.kt

.../java/org/mozilla/fenix/settings/AccessibilityFragment.kt

app/src/main/java/org/mozilla/fenix/settings/PhoneFeature.kt

...mozilla/fenix/settings/RadioSearchEngineListPreference.kt

...ava/org/mozilla/fenix/settings/SitePermissionsFragment.kt

...nix/settings/SitePermissionsManagePhoneFeatureFragment.kt

.../org/mozilla/fenix/settings/TrackingProtectionFragment.kt

...la/fenix/settings/quicksettings/QuickSettingsComponent.kt

...lla/fenix/settings/sharedpreferences/BooleanPreference.kt

...lla/fenix/settings/sharedpreferences/PreferencesHolder.kt

...sharedpreferences/SitePermissionsRulesActionPreference.kt

app/src/main/java/org/mozilla/fenix/utils/Settings.kt

...fenix/settings/sharedpreferences/BooleanPreferenceTest.kt

...edpreferences/SitePermissionsRulesActionPreferenceTest.kt

app/src/test/java/org/mozilla/fenix/utils/SettingsTest.kt