Autoclick: Fix mouse disconnect logic

Trigger the input device observer when the Autoclick panel is initiated.
This fixes the bug of the panel not hiding itself the first time the
mouse is disconnected

Bug: 439772850
Test: AutoclickControllerTest
Flag: com.android.server.accessibility.enable_autoclick_indicator
Change-Id: I52fddb7bc86ae74ce938c409b10f18f0d22c7903