Fix inconsistent scale when setting magnificaotion config

We used to use MagnificationScaleProvider to retrive the
scale when transitioning the mode, which is incorrect
because the provider only persists the scale changed by users.
If the scale is changed by public api, then the scale will
become inconsistent.

To fix it we choose the scale based on the target  mode.
We also fix that mode transition without animation should be
considered as a transition case.

We also add more log for flaky CTS debugging.

Bug: 218792845
Test: atest MagnificationProcessorTest
      atest com.android.server.accessibility.magnification
Change-Id: I47f49345ce46f726d6e06e203110ef793f35c76e