[PiP2] Properly scale corner radii while animating

If a task leash is scaled by some factor x,
we need to scale the corner raddi by a factor of (1/x)
to make the rounded corners look visually invariant.

We can enforce this during pinching (i.e. schedulerUserResizePip)
and during the resize animation in PipResizeAnimator.

Bug: 397958290
Flag: com.android.wm.shell.enable_pip2
Test: double tap to resize
Test: pinch PiP to resize

Change-Id: I3b4dcdea7e2e5362d2e6504a49de06d73895cb6a