Make the position of the mirror content the same as the real one

When the magnification scale is 1x, we can find that position of
the mirror content has a bias with the real content on the screen.
To fix it, we offset the the mirror view with the margin of
mirror surface view.

Bug: 148836275
Test: adb shell settings put secure window_magnification 1
Change-Id: I32e019f44183081819e06e056c080442458e5137