Fix clang-tidy warnings in aapt and aapt2.

* Add explicit keyword to conversion constructors.
* Add NOLINT(implicit) comments for implicit conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
* Use const reference type to avoid unnecessary copy.
Bug: 30413862
Test: build with WITH_TIDY=1

Change-Id: Id6d21961f313a1ad92b15a37fdaa5be9e8ab48e1
Merged-In: Id6d21961f313a1ad92b15a37fdaa5be9e8ab48e1
diff --git a/tools/aapt/XMLNode.h b/tools/aapt/XMLNode.h
index b9e5cd5..d9d86ec 100644
--- a/tools/aapt/XMLNode.h
+++ b/tools/aapt/XMLNode.h
@@ -176,7 +176,7 @@
     XMLNode(const String8& filename, const String16& s1, const String16& s2, bool isNamespace);
     
     // Creating a CDATA node.
-    XMLNode(const String8& filename);
+    explicit XMLNode(const String8& filename);
     
     status_t collect_strings(StringPool* dest, Vector<uint32_t>* outResIds,
             bool stripComments, bool stripRawValues) const;