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/mirror/class.cc b/runtime/mirror/class.cc
index 6bee3cf..8a7defd 100644
--- a/runtime/mirror/class.cc
+++ b/runtime/mirror/class.cc
@@ -25,9 +25,9 @@
 #include "class_ext.h"
 #include "class_linker-inl.h"
 #include "class_loader.h"
+#include "dex/dex_file-inl.h"
+#include "dex/dex_file_annotations.h"
 #include "dex_cache.h"
-#include "dex_file-inl.h"
-#include "dex_file_annotations.h"
 #include "gc/accounting/card_table-inl.h"
 #include "handle_scope-inl.h"
 #include "subtype_check.h"