Migrates Flags.enableConnectedDisplaysWindowDrag to use DesktopExperienceFlag

Bug: 407921704
Test: atest WMShellUnitTests:DisplayControllerTests
Test: atest WMShellUnitTests:DesktopTasksControllerTest
Test: atest WMShellUnitTests:DesktopModeWindowDecorViewModelTests
Flag: EXEMPT - changing flag infra
Change-Id: I2972eb8f4a62137a210471225cb045df183677d8
3 files changed