Determine whether to support activities in multi window (3/n)

Add flags to support device settings for support activities in multi
window.

Will use the new flag to determine whether an activity can be shown in
multi window.

Bug: 176061101
Test: atest WmTests:ActivityTaskManagerServiceTests
Change-Id: I2808b0bbf2ce436f972a0239ece7d6a781af035b