Add "passwordInput" attribute to case tag of Keyboard

This change also introduces number password (a.k.a. PIN) layout. The
text password layout will follow.

Bug: 3384942
Change-Id: I50b5e413e47a28d5285fd0468115e11ce46c7f18
diff --git a/java/res/values/attrs.xml b/java/res/values/attrs.xml
index f5babd3..6589278 100644
--- a/java/res/values/attrs.xml
+++ b/java/res/values/attrs.xml
@@ -168,6 +168,7 @@
             <enum name="web" value="4" />
             <enum name="phone" value="5" />
         </attr>
+        <attr name="passwordInput" format="boolean" />
         <attr name="hasSettingsKey" format="string" />
         <attr name="voiceKeyEnabled" format="string" />
         <attr name="hasVoiceKey" format="string" />