Add support for search modifier fallbacks

Fixes a bug in where kcm fallbacks with search based modifiers could
not activate since PhoneWindowManager would consume all search events.
This prevented the InputDispatcher from generating the fallback.

This change modifies the behavior so InputDispatcher handles whether
the search-based event will attempt to generate a fallback.

Bug: 384113980
Test: atest InputDispatcherTest

Flag: com.android.hardware.input.fix_search_modifier_fallbacks

Change-Id: Ib7eca10f00ec93fd46a93396b7908ff925dd705b