Override hashCode in AnimatableScaleMatrix

This class is used in PhysicsAnimator as a key in a hashmap. We already
override equals, also override hashCode for it to have matching
behavior.

Bug: 349845968
Test: atest WMShellRobolectricTests:com.android.wm.shell.bubbles.animation.AnimatableScaleMatrixTest
Test: atest  WMShellMultivalentTestsOnDevice:com.android.wm.shell.bubbles.animation.AnimatableScaleMatrixTest
Flag: EXEMPT bugfix
Change-Id: I56625f616426e3aa01d3c413de45a6f340c7f018