ART: Fix tidy warnings

Switch to char versions of find variants.

Add "explicit" constructor variants or refactor and
remove defaults.

Use const references.

Bug: 32619234
Test: m test-art-host
Change-Id: I970cc2f47d6cf8f0c74104b994b075b2fafb3d45
diff --git a/dexlayout/dexlayout.cc b/dexlayout/dexlayout.cc
index 2b30a1b..aa80655 100644
--- a/dexlayout/dexlayout.cc
+++ b/dexlayout/dexlayout.cc
@@ -1527,7 +1527,7 @@
   // Output dex file.
   if (options_.output_dex_directory_ != nullptr) {
     std::string output_location(options_.output_dex_directory_);
-    size_t last_slash = dex_file->GetLocation().rfind("/");
+    size_t last_slash = dex_file->GetLocation().rfind('/');
     output_location.append(dex_file->GetLocation().substr(last_slash));
     DexWriter::OutputDexFile(*header, output_location.c_str());
   }