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
diff --git a/tools/aapt/CrunchCache.cpp b/tools/aapt/CrunchCache.cpp
index 0d574cf..7b8a576 100644
--- a/tools/aapt/CrunchCache.cpp
+++ b/tools/aapt/CrunchCache.cpp
@@ -94,7 +94,7 @@
     delete dw;
 }
 
-bool CrunchCache::needsUpdating(String8 relativePath) const
+bool CrunchCache::needsUpdating(const String8& relativePath) const
 {
     // Retrieve modification dates for this file entry under the source and
     // cache directory trees. The vectors will return a modification date of 0