Create dex subdirectory

Move all the DexFile related source to a common subdirectory dex/ of
runtime.

Bug: 71361973
Test: make -j 50 test-art-host
Change-Id: I59e984ed660b93e0776556308be3d653722f5223
diff --git a/runtime/oat_file_assistant.cc b/runtime/oat_file_assistant.cc
index 8707e73..240030c 100644
--- a/runtime/oat_file_assistant.cc
+++ b/runtime/oat_file_assistant.cc
@@ -28,7 +28,7 @@
 #include "base/stl_util.h"
 #include "class_linker.h"
 #include "compiler_filter.h"
-#include "dex_file_loader.h"
+#include "dex/dex_file_loader.h"
 #include "exec_utils.h"
 #include "gc/heap.h"
 #include "gc/space/image_space.h"