[1/n] Move getPreferredLaunchTaskDisplayArea to LaunchParamsUtil

Move logic of resolving launch TaskDisplayArea to common utils for reuse
in DesktopModeLaunchParamsModifier.

This is the first step to decide whether desktop is visible when
TaskDisplayArea is set to freeform with no empty tasks.

Flag: EXEMPT refactor
Bug: 401564801
Test: atest TaskLaunchParamsModifierTests
Change-Id: I8dba79e7e46c5494e1ddd81cc8ed57a75fee9127