Move desktop-first policy from Shell to LPM

This CL moves desktop-first policy around windowing mode decisions from
handleRequest to LaunchParamsModifier so that the launch windowing mode
by ActivityOptions can be respected (and there will be no double
windowing mode change on an app launch).
Note that this change is exclusive for desktop-first and a few
touch-first policies remain in handleRequest.

Flag: com.android.window.flags.enable_desktop_first_policy_in_lpm
Bug: 427828063
Bug: 431866074
Test: DesktopTasksControllerTest
Test: DesktopModeLaunchParamsModifierTests
Change-Id: Ia7a0c0b5b39b4c8b5abe180615d205b96f433fcf