Add functional test for drag-to-maximize

This CL adds a functional test for drag-to-maximize. Note that the test
assumes that the feature is enabled on the device. If not, the test is
skipped.

Bug: 378396431
Flag: EXEMPT add test
Test: MaximizeAppWindowWithDragToTopDragZoneTest
Change-Id: I957b57b517b70bbbacd46aa675b5e66bf78ea89e