Do not dispatch system UI visibility during traversal

Otherwise, mRecomputeGlobalAttributes set within the callbacks might be
cleared in the traversal.

This CL also prevents dispatching non-existing insets sources to the
client. For example, if a display doesn't have a navigation bar, the
insets state dispatched by window manager won't contain the navigation
bar source. So that WindowInsets.isVisible(ITYPE_NAVIGATION_BAR) returns
false on such display.

Fix: 155787445
Fix: 155796402
Test: atest WindowInsetsControllerTests InsetsAnimationControlImplTest
Change-Id: I3104191b34c08e14ffb31d7228c832a84629a97b