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/runtime/base/variant_map_test.cc b/runtime/base/variant_map_test.cc
index ccb22eb..93336e0 100644
--- a/runtime/base/variant_map_test.cc
+++ b/runtime/base/variant_map_test.cc
@@ -107,8 +107,8 @@
   fmFilled.Set(FruitMap::Orange, 555.0);
   EXPECT_EQ(size_t(2), fmFilled.Size());
 
-  // Test copy constructor
-  FruitMap fmEmptyCopy(fmEmpty);
+  // Test copy constructor (NOLINT as a reference is suggested, instead)
+  FruitMap fmEmptyCopy(fmEmpty);  // NOLINT
   EXPECT_EQ(size_t(0), fmEmptyCopy.Size());
 
   // Test copy constructor