Move dexpreopt.Script to android.RuleBuilder

Move dexpreopt.Script to android.RuleBuilder so that the builder
style can be used in more places.  Also add tests for it.

Test: rule_builder_test.go
Change-Id: I92a963bd112bf033b08899e930094b908acfcdfd
diff --git a/dexpreopt/Android.bp b/dexpreopt/Android.bp
index b832529..c5f24e2 100644
--- a/dexpreopt/Android.bp
+++ b/dexpreopt/Android.bp
@@ -4,12 +4,12 @@
     srcs: [
         "config.go",
         "dexpreopt.go",
-        "script.go",
     ],
     testSrcs: [
         "dexpreopt_test.go",
     ],
     deps: [
         "blueprint-pathtools",
+        "soong-android",
     ],
-}
\ No newline at end of file
+}