Fix google-explicit-constructor warnings in frameworks/rs.

 * Declare explicit conversion constructors.
 * Add NOLINT to implicit conversion constructors.

 Bug: 28341362
 Test: build with clang-tidy

Change-Id: If5114de668c1c8946b8fca9cee4b2b14f95be5f1
diff --git a/rsScript.h b/rsScript.h
index e336f07..39620c1 100644
--- a/rsScript.h
+++ b/rsScript.h
@@ -98,7 +98,7 @@
     };
     Hal mHal;
 
-    Script(Context *);
+    explicit Script(Context *);
     virtual ~Script();
 
     struct Enviroment_t {