Fix split screen test case failure

5af1f6704d88d4972, change to use isSplitScreenVisible for related logic.
This CL updates the test case with the change together.

Bug: 262544588
Test: atest com.android.wm.shell.splitscreen
Change-Id: I5713effd96d972b31fad963ed1b966a494ff7823
1 file changed