Utilize StateListDrawable for key preview background

java/res/drawable/keyboard_key_feedback.xml

java/res/drawable/keyboard_key_feedback_ics.xml

java/res/drawable/keyboard_key_feedback_left_ics.xml

java/res/drawable/keyboard_key_feedback_right_ics.xml

java/res/layout/key_preview.xml

java/res/layout/key_preview_ics.xml

java/res/values/attrs.xml

java/res/values/styles.xml

java/src/com/android/inputmethod/keyboard/KeyboardView.java

.../android/inputmethod/keyboard/internal/KeyDrawParams.java

...d/inputmethod/keyboard/internal/KeyPreviewDrawParams.java