[PiP on Desktop] Fix drag getting triggered on dismiss button.

Further fix will come to avoid hit on dismiss button getting routed to
drag logic due to drag area and dismiss button overlap, but this CL will
prevent PiP from being resized by accident.

Bug: 397765476
Test: Manually test that touching dismiss button doesn't resize PiP.
Flag: com.android.window.flags.enable_desktop_windowing_pip
Change-Id: I8f90eacfd13326f1c6ff710bee6f6c73d1cfcbb9