Shorten title name so as not to hit char limit.

This is a follow up CL to my previous CL [1], which tried to rename a
settings item "Add virtual keyboard" but ended up with hitting char
limit in many languages.  We decided to use "Manage keyboards" instead
so as not to hit char limit.

 [1]: Id2ae61519152bbe622aa5915f728a4cbbc49e078
      611410a8c4b55b0fc6fde3e718f028335dea41d8

Bug: 27543291
Bug: 27959401
Change-Id: I6e4795f8c4dbe9857d036ca19689e05658aa0640
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 46e96d3..cb3b81e 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -3626,8 +3626,8 @@
     <string name="virtual_keyboard_category">Virtual keyboard</string>
     <!-- Title for the 'available virtual keyboard' preference sub-screen. [CHAR LIMIT=35] -->
     <string name="available_virtual_keyboard_category">Available virtual keyboard</string>
-    <!-- Title for the button to trigger the 'Add or edit virtual keyboards' preference sub-screen. [CHAR LIMIT=35] -->
-    <string name="add_virtual_keyboard">Add or edit virtual keyboards</string>
+    <!-- Title for the button to trigger the 'Manage keyboards' preference sub-screen, where the user can turn on/off installed virtual keyboards.[CHAR LIMIT=35] -->
+    <string name="add_virtual_keyboard">Manage keyboards</string>
     <!-- Title for the 'keyboard assistance' preference category. [CHAR LIMIT=35] -->
     <string name="keyboard_assistance_category">Keyboard assistance</string>
     <!-- Title for the 'physical keyboard' settings screen. [CHAR LIMIT=35] -->