LineageParts: Add support for customising navbar app switch long press action

*) Also fixes bug where we weren't initializing app switch long press
   setting to config_longPressOnAppSwitchBehavior (even for hardware keys).
   I've verified that the config is set to split screen in lineage-sdk.

Change-Id: I3af7bcf6402cecbb6843d50f7a1000af84e9e53d
diff --git a/res/xml/button_settings.xml b/res/xml/button_settings.xml
index f0efc41..bf15b56 100644
--- a/res/xml/button_settings.xml
+++ b/res/xml/button_settings.xml
@@ -63,6 +63,14 @@
             android:entryValues="@array/hardware_keys_action_values"
             android:persistent="false" />
 
+        <ListPreference
+            android:key="navigation_app_switch_long_press"
+            android:dialogTitle="@string/navigation_bar_app_switch_long_press_title"
+            android:title="@string/navigation_bar_app_switch_long_press_title"
+            android:entries="@array/hardware_keys_action_entries"
+            android:entryValues="@array/hardware_keys_action_values"
+            android:persistent="false" />
+
     </PreferenceCategory>
 
     <PreferenceCategory