Style panel with Material designs (1/n)

We apply Theme.SystemUI to the window context for
WindowMagnificationController to follow the theme color configurations
in SystemUI.

The following components are styled to follow Material designs in this
modification:
1. The background of the settings panel
2. All text titles

The margin and padding for coresponding layouts and views are fixed and defined in the
file "dimens.xml".

Bug: 257272333
Test: manual - attach screenshots with the bug
Change-Id: I11646fe5739eaf48d9e12e432a796bec7d97cdd7