Move auto correction thresthold to the native code

java/src/com/android/inputmethod/latin/AutoCorrection.java

java/src/com/android/inputmethod/latin/BinaryDictionary.java

java/src/com/android/inputmethod/latin/Utils.java

...utmethod/latin/spellcheck/AndroidSpellCheckerService.java

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

native/src/correction.cpp

native/src/correction.h

.../src/com/android/inputmethod/latin/EditDistanceTests.java