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/dex/inline_method_analyser.cc b/compiler/dex/inline_method_analyser.cc
index ba2ebd9..b0f025d 100644
--- a/compiler/dex/inline_method_analyser.cc
+++ b/compiler/dex/inline_method_analyser.cc
@@ -511,7 +511,7 @@
 }
 
 bool InlineMethodAnalyser::IsSyntheticAccessor(MethodReference ref) {
-  const DexFile::MethodId& method_id = ref.dex_file->GetMethodId(ref.index);
+  const dex::MethodId& method_id = ref.dex_file->GetMethodId(ref.index);
   const char* method_name = ref.dex_file->GetMethodName(method_id);
   // javac names synthetic accessors "access$nnn",
   // jack names them "-getN", "-putN", "-wrapN".