Do not let snapshot window control the bar

But allow splash screen window to control the bar.
Unlike snapshot starting window, all system bar corresponding attributes
are read from app theme, so ideally the initial value should equals to
the first activity main window. Even if the activity set another theme,
it should only produce an one-time transition.
(Ref: I3d7ba6b7d78c0508ddeccbf1d3408d723bd8e2c0)

Bug: 261247891
Test: atest WindowStateTests
Change-Id: I957e1eddcfa3f7b873f7a9b32eeaf69db5927b00