themes: convert theme copying to a golang module

Change-Id: I0a1e4b79109cf9db93acb0575200f4ec8f72d3a2
diff --git a/Android.bp b/Android.bp
index 5afdbfd..ffb4f1a 100755
--- a/Android.bp
+++ b/Android.bp
@@ -23,7 +23,8 @@
         "soong-cc"
     ],
     srcs: [
-        "libaosprecovery_defaults.go"
+        "libaosprecovery_defaults.go",
+        "soong/makevars.go"
     ],
     pluginFor: ["soong_build"]
 }