[RESTRICT AUTOMERGE] Check windowing mode instead of divider window to verify split screen

AccessibilityWindowQueryTest#testWindowDockAndUndock_dividerWindowAppearsAndDisappears
checks the existence of a divider window to know if it's in split
screen or not. However, the divider is an implementation detail of
system ui, and some system UI doesn't have it.

This CL replaces a check of divider window presence with activity's
windowing mode to verify it.

This change also renames the corresponding test because now that the
test is not related to divider window.

Bug: 170064014
Bug: 170320826
Test: AccessibilityWindowQueryTest#testToggleSplitScreen on eve and crosshatch
Change-Id: Iffed2a449cb4e21a488e8b45565bb0945dce2754
Merged-In: Iffed2a449cb4e21a488e8b45565bb0945dce2754
1 file changed