Support per-Key and per-Keyboard key visual attributes

This change refactors KeyDrawParams and KeyPreviewDrawParams to
separate KeyVisualAttributes.

Change-Id: I4de549eef303e1debe4b8f84668e042445fc18da
diff --git a/java/res/values/attrs.xml b/java/res/values/attrs.xml
index b659763..c8f6435 100644
--- a/java/res/values/attrs.xml
+++ b/java/res/values/attrs.xml
@@ -49,6 +49,8 @@
         <attr name="keyPopupHintLetterPadding" format="dimension" />
         <!-- Right padding of shifted letter hint to the edge of the key.-->
         <attr name="keyShiftedLetterHintPadding" format="dimension" />
+        <!-- Blur radius of key text shadow. -->
+        <attr name="keyTextShadowRadius" format="float" />
 
         <!-- Layout resource for key press feedback.-->
         <attr name="keyPreviewLayout" format="reference" />
@@ -320,7 +322,6 @@
         <!-- Color to use for the label in a key. -->
         <attr name="keyTextColor" format="color" />
         <attr name="keyTextShadowColor" format="color" />
-        <attr name="keyTextShadowRadius" format="float" />
         <!-- Color to use for the label in a key when in inactivated state. -->
         <attr name="keyTextInactivatedColor" format="color" />
         <!-- Key hint letter (= one character hint label) color -->