Add flag for perferred input device logic in audio policy engine

Add a flag allowing to skip the preferred device selection in
Engine::getInputDeviceForAttributes() in a context like
getInputForAttributes() where it should be ignored.

Test: make
Flag: com.android.media.audioserver.conditionally_ignore_preferred_input_device
Bug: 303079083
Change-Id: I0f83fe2528f2ab888bc1d3b8aff127f838d612db