Use string attribute for icon name

java/res/values/attrs.xml

java/res/values/keyboard-icons-black.xml

java/res/values/keyboard-icons-ics.xml

java/res/values/keyboard-icons-white.xml

java/res/xml-sw600dp/key_styles_common.xml

java/res/xml-sw768dp/key_styles_common.xml

java/res/xml/key_styles_common.xml

java/res/xml/key_styles_enter.xml

java/res/xml/key_styles_number.xml

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

.../android/inputmethod/keyboard/internal/KeySpecParser.java

.../com/android/inputmethod/keyboard/internal/KeyStyles.java

...droid/inputmethod/keyboard/internal/KeyboardIconsSet.java

...roid/inputmethod/keyboard/internal/KeyboardLabelsSet.java

.../inputmethod/keyboard/internal/KeySpecParserCsvTests.java

...oid/inputmethod/keyboard/internal/KeySpecParserTests.java

tools/makelabel/res/values/donottranslate-more-keys.xml