Calculates the window height fraction on screen by the draggable bounds for magnification switch button

In the previous change ag/14776093, the window height fraction used
"windowHeightFraction = (float) mParams.y / mWindowHeight;". And it
causes the  Y-position deviated after the rotation is changed.
To correct this, we used the draggable bounds to calculate the window
height fraction.
See b/189715285#comment3

Bug: 189715285
Test: atest MagnificationModeSwitchTest
Change-Id: I1adcea12f0a96c64c9c6e386dc2feb8e3a9ffcf3
2 files changed