Add tools:keep to plugin prefs to avoid false-positive lint

res/xml/findmyphoneplugin_preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
+    tools:keep="@xml/findmyphoneplugin_preferences">
 
     <Preference
         android:key="@string/findmyphone_preference_key_ringtone"

res/xml/mousepadplugin_preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
+    tools:keep="@xml/mousepadplugin_preferences">
 
     <ListPreference
         android:id="@+id/mousepad_double_tap_preference"

res/xml/mprisplugin_preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
+    tools:keep="@xml/mprisplugin_preferences">
 
     <ListPreference
         android:id="@+id/mpris_time_preference"

res/xml/remotekeyboardplugin_preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
+    tools:keep="@xml/remotekeyboardplugin_preferences">
 
     <CheckBoxPreference
         android:id="@+id/remotekeyboard_editing_only"

res/xml/sftpplugin_preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
-<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+<PreferenceScreen xmlns:tools="http://schemas.android.com/tools"
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    tools:keep="@xml/sftpplugin_preferences">
     <PreferenceCategory
         android:key="@string/sftp_preference_key_preference_category"
         android:title="@string/sftp_preference_detected_sdcards"

res/xml/shareplugin_preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
+    tools:keep="@xml/shareplugin_preferences">
 
     <CheckBoxPreference
         android:id="@+id/share_destination_customize"

res/xml/telephonyplugin_preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
-<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+<PreferenceScreen xmlns:tools="http://schemas.android.com/tools"
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    tools:keep="@xml/telephonyplugin_preferences">
 
     <EditTextPreference
         android:dialogMessage="@string/telephony_pref_blocked_dialog_desc"