SF: Clean up input info calculations

This CL simplifies the calculation of the input transform and frame for
Layers.

It also switches the calculations to use floats rather than intergers
for greater precesion when scaling.

Bug: 200787840
Bug: 179274888
Test: atest libgui_test
Change-Id: Ia1ed53b669caa867e5b98e72d5d71ed615222f8f