Add separate key hysteresis distance for sliding modifier input

java/res/values/attrs.xml

java/res/values/config.xml

java/res/values/styles.xml

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

...rc/com/android/inputmethod/keyboard/MainKeyboardView.java

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