Update synonyms and fix some issues related to them

- update synonyms definitions
- fix issue with L release regression for indexing "Backup & reset":
was missing the marker interface "Indexable"
- fix non working synonyms for "Language & input": their declaration
was done in the XML preference file but was not used because the
SearchIndexProvider was built "by hand"

See bug #17474866 Settings search synonyms needs an update

Change-Id: Iceab71a0e3214f3a8ba0dcd77756c3632609c5ce
diff --git a/res/xml/language_settings.xml b/res/xml/language_settings.xml
index a6f01aa..5cc8a4a 100644
--- a/res/xml/language_settings.xml
+++ b/res/xml/language_settings.xml
@@ -31,7 +31,6 @@
     <PreferenceScreen
             android:key="spellcheckers_settings"
             android:title="@string/spellcheckers_settings_title"
-            settings:keywords="@string/keywords_spell_checker"
             android:persistent="false"
             />
 
@@ -43,8 +42,7 @@
 
     <PreferenceCategory
             android:key="keyboard_settings_category"
-            android:title="@string/keyboard_settings_category"
-            settings:keywords="@string/keywords_keyboard_and_ime">
+            android:title="@string/keyboard_settings_category">
 
         <PreferenceScreen
                 android:key="current_input_method"
@@ -68,14 +66,12 @@
         <PreferenceScreen
                 android:key="voice_input_settings"
                 android:title="@string/voice_input_settings_title"
-                settings:keywords="@string/keywords_voice_input"
                 android:fragment="com.android.settings.voice.VoiceInputSettings"
                 />
 
         <PreferenceScreen
                 android:key="tts_settings"
                 android:title="@string/tts_settings_title"
-                settings:keywords="@string/keywords_text_to_speech_output"
                 android:fragment="com.android.settings.tts.TextToSpeechSettings"
                 />