Read system decor support status from WM

There is no way to add FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS to
hardware or simulated displays, so wallpaper, IME and nav bar were
not showing up even when desktop mode developer option was enabled.

Bug: 123199549
Bug: 125007644
Bug: 124073468
Bug: 124073384
Test: Enable force desktop mode, reboot, create simulated display
Change-Id: Id6f2f3746407467f20c1f26e735b84653e34625d