[Toast] Switch to using device config to control keyboard sync.

Bug: 234812580
Test: followed the existing pattern and tested by manually setting and
unsetting the flag through command line - `adb shell device_config put
launcher enable_web_suggest_on_default_browser <true|false>`

Change-Id: Idd479e93b628b78fdf55d826c56f69c5cfdaf46e