Move the unit test classes for PiP

For classes we moved from PiP1 package to common.pip, the unit test
classes were not moved together.

What's next

There are certain class we copied from pip1 to pip2 without copying also
the unit tests, including

- PipController
- PipResizeGestureHandler
- PipTouchHandler
- PipTouchState

Would do a follow up CL on that

Flag: com.android.wm.shell.enable_pip2
Bug: 376133026
Test: atest WMShellUnitTests
Change-Id: Ifa6d5cadf5dab2524141f9e418c1d62eb0ea473f