When DeviceConfig/FeatureFlag value is different than the previous

value, refresh icon cache

Bug: 135638690
Bug: 138964490

Test: manually toggled feature flag UI on/off
$ adb shell device_config put launcher APP_SEARCH_IMPROVEMENTS [true|false]
when launcher is in foreground and also when it is in the background

Afterwards, saw if "bank" would show BofA app or not

Change-Id: I98b62bd07b14a225168217d7eb9bfdfc7f74435d