Hold the status bar off the window's top, not the content view's

[andiwand]

#672 moved the banner into the decor's stack, so it sits above the content view and above the bar an action mode raises. The inset padding stayed behind on main_root, which is inside the content view.

So the status bar was held off the wrong thing. On a Pixel 9 Pro the window read:

[0,0][960,150]     ad_container      <- behind the clock and the status icons
[0,150][960,2142]  content
[0,303][960,2142]  main_root's child <- padded again, a dead strip under the ad

The padding now goes on the stack that holds the banner, the action mode's bar and the content, so the status bar is held off once for all three:

[0,0][960,2142]    action_bar_root   <- padded 153 at the top
[0,153][960,303]   ad_container
[0,303][960,447]   action_mode_bar
[0,447][960,573]   editing_tools
[0,573][960,2142]  document_container

Confirmed on a Pixel 9 Pro, on the landing screen and in a pdf's markup mode.