Add DexFileLoader class

Added DexFileLoader class, moved functionality from DexFile there:
- Multidex loading logic
- DexFile opening logic for Zip and etc
- Some other helpers

Bug: 63756964
Test: test-art-host

Change-Id: Ic3dfa458947d4b69912dea5cdd836e7e8f55061c
diff --git a/openjdkjvmti/ti_class.cc b/openjdkjvmti/ti_class.cc
index daf4a8b..5f29416 100644
--- a/openjdkjvmti/ti_class.cc
+++ b/openjdkjvmti/ti_class.cc
@@ -43,6 +43,7 @@
 #include "class_table-inl.h"
 #include "common_throws.h"
 #include "dex_file_annotations.h"
+#include "dex_file_loader.h"
 #include "events-inl.h"
 #include "fixed_up_dex_file.h"
 #include "gc/heap-visit-objects-inl.h"
@@ -106,12 +107,12 @@
   }
   uint32_t checksum = reinterpret_cast<const art::DexFile::Header*>(map->Begin())->checksum_;
   std::string map_name = map->GetName();
-  std::unique_ptr<const art::DexFile> dex_file(art::DexFile::Open(map_name,
-                                                                  checksum,
-                                                                  std::move(map),
-                                                                  /*verify*/true,
-                                                                  /*verify_checksum*/true,
-                                                                  &error_msg));
+  std::unique_ptr<const art::DexFile> dex_file(art::DexFileLoader::Open(map_name,
+                                                                        checksum,
+                                                                        std::move(map),
+                                                                        /*verify*/true,
+                                                                        /*verify_checksum*/true,
+                                                                        &error_msg));
   if (dex_file.get() == nullptr) {
     LOG(WARNING) << "Unable to load modified dex file for " << descriptor << ": " << error_msg;
     art::ThrowClassFormatError(nullptr,