Add base scenario test for desktop mode window drag.

Adding two base scenarios two test the following:
1) Single app window drag.
2) Multiple overlapping windows drag.
Video recording of CUJ test here: b/339585412#comment2

Bug: 339585412
Test: atest DragAppWindowMultiWindow
Flag: com.android.window.flags.enable_desktop_windowing_mode

Change-Id: I1c9d79795e1e7c6ccde3e1855ec928d927d6a640
Signed-off-by: Devarshi Bhatt <devarshimb@google.com>