fix(magnification): fix NPE from using deprecated instrumentation

Somehow androidx.test.platform.app.InstrumentationRegistry() was
returning null. So we retreive it fresh every time, and use the
non-deprecated class.

Fix: 308152609
Test: atest
packages/SystemUI/tests/src/com/android/systemui/accessibility/WindowMagnificationAnimationControllerTest.java
Flag: NA

Change-Id: Iee86dd9fa58e03bbc2b475fa72a08a6fd88e276f