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/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index 11c9031..dabe07f 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -59,11 +59,11 @@
 #include "debug/elf_debug_writer.h"
 #include "debug/method_debug_info.h"
 #include "dexlayout.h"
+#include "dex/dex_file-inl.h"
 #include "dex/quick_compiler_callbacks.h"
 #include "dex/verification_results.h"
 #include "dex2oat_options.h"
 #include "dex2oat_return_codes.h"
-#include "dex_file-inl.h"
 #include "driver/compiler_driver.h"
 #include "driver/compiler_options.h"
 #include "driver/compiler_options_map-inl.h"