PrintSpooler: Add bottom padding to preview area

When edge-to-edge support was added to print preview, the new top insets
pushed down the preview area.  If there are more pages than can fit on a
single screen, the selection button on the last page is no longer
reachable.  Restore this by inserting bottom padding equal to the insets
that were previously applied on the container; this ensures the bottom
active content can be scrolled up above the navigation bar.

Bug: 406287680
Test: Manually print multi-page docs in various orientations
Flag: EXEMPT bugfix
Change-Id: Ib59c5df8898186c6ec9affbe4119731e2d4c96e4