fix(cts): fix the test based on flag create_windowless_window_magnifier

The cts test failed after enabling the flag since we were performing
last `enableWindowMagnificationInternal` in `onAnimationUpdate`, but
checking the flag that will be updated in `ValueAnimator#endAnimation`
in `enableWindowMagnificationInternal`.
Add `enableWindowMagnificationInternal` in `onAnimationEnd` to guarantee that window magnification mirror and source bounds are updated to the latest state
when the animation finishes.

Bug: 323528222
Test: atest AccessibilityMagnificationTest
      atest WindowMagnificationControllerTest
      atest WindowMagnificationControllerWindowlessMagnifierTest
      atest WindowMagnificationAnimationControllerTest
Flag: ACONFIG com.android.systemui.create_windowless_window_magnifier DEVELOPMENT
Change-Id: Ibd102cfd330583574e63d8e128ef99e66270dcfc