Introduce KeyboardCodesSet.java and remove keycodes.xml

Change-Id: Icfd6d06f47425aa037682d22c895548ba6f047d8
diff --git a/java/res/values/attrs.xml b/java/res/values/attrs.xml
index 39d50e3..d574b9e 100644
--- a/java/res/values/attrs.xml
+++ b/java/res/values/attrs.xml
@@ -229,10 +229,14 @@
     </declare-styleable>
 
     <declare-styleable name="Keyboard_Key">
-        <!-- The unicode value that this key outputs. -->
-        <attr name="code" format="integer" />
-        <!-- The alternate unicode value that this key outputs while typing. -->
-        <attr name="altCode" format="integer" />
+        <!-- The unicode value that this key outputs.
+             Code value represented in hexadecimal prefixed with "0x" or code value reference using
+             "!code/<code_name>" notation. -->
+        <attr name="code" format="string" />
+        <!-- The alternate unicode value that this key outputs while typing.
+             Code value represented in hexadecimal prefixed with "0x" or code value reference using
+             "!code/<code_name>" notation. -->
+        <attr name="altCode" format="string" />
         <!-- The keys to display in the more keys keyboard. -->
         <attr name="moreKeys" format="string" />
         <!-- The keys to display in the more keys keyboard in addition to moreKeys.