Calculates the window height fraction on screen by the draggable bounds for...

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