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/rsScriptGroupBase.h b/rsScriptGroupBase.h
index 00ae6c6..f79f08f 100644
--- a/rsScriptGroupBase.h
+++ b/rsScriptGroupBase.h
@@ -8,7 +8,7 @@
 
 class ScriptGroupBase : public ObjectBase {
  public:
-  ScriptGroupBase(Context* rsc) : ObjectBase(rsc) {}
+  explicit ScriptGroupBase(Context* rsc) : ObjectBase(rsc) {}
   virtual ~ScriptGroupBase() {}
 
   virtual void serialize(Context *rsc, OStream *stream) const {}