ART: Move dex structs into own header

Separating out the structs from DexFile allows them to be forward-
declared, which reduces the need to include the dex_file header.

Bug: 119869270
Test: m
Change-Id: I32dde5a632884bca7435cd584b4a81883de2e7b4
diff --git a/compiler/driver/compiler_driver-inl.h b/compiler/driver/compiler_driver-inl.h
index 63dcb46..ec2e38b 100644
--- a/compiler/driver/compiler_driver-inl.h
+++ b/compiler/driver/compiler_driver-inl.h
@@ -57,7 +57,7 @@
     const DexCompilationUnit* mUnit) {
   DCHECK_EQ(dex_cache->GetDexFile(), mUnit->GetDexFile());
   DCHECK_EQ(class_loader.Get(), mUnit->GetClassLoader().Get());
-  const DexFile::MethodId& referrer_method_id =
+  const dex::MethodId& referrer_method_id =
       mUnit->GetDexFile()->GetMethodId(mUnit->GetDexMethodIndex());
   return ResolveClass(soa, dex_cache, class_loader, referrer_method_id.class_idx_, mUnit);
 }