Fix updating the shift state upon backspace

java/src/com/android/inputmethod/event/DeadKeyCombiner.java

java/src/com/android/inputmethod/event/Event.java

...droid/inputmethod/event/HardwareKeyboardEventDecoder.java

...c/com/android/inputmethod/keyboard/EmojiPalettesView.java

.../android/inputmethod/keyboard/KeyboardActionListener.java

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

...om/android/inputmethod/keyboard/MoreKeysKeyboardView.java

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

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

.../com/android/inputmethod/latin/inputlogic/InputLogic.java

tests/src/com/android/inputmethod/latin/InputTestsBase.java

tests/src/com/android/inputmethod/latin/ShiftModeTests.java