Make CodeItem fields private

Make code item fields private and use accessors. Added a hand full of
friend classes to reduce the size of the change.

Changed default to be nullable and removed CreateNullable.
CreateNullable was a bad API since it defaulted to the unsafe, may
add a CreateNonNullable if it's important for performance.

Motivation:
Have a different layout for code items in cdex.

Bug: 63756964
Test: test-art-host-gtest
Test: test/testrunner/testrunner.py --host
Test: art/tools/run-jdwp-tests.sh '--mode=host' '--variant=X32' --debug

Change-Id: I42bc7435e20358682075cb6de52713b595f95bf9
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 55fa632..45b7618 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -4317,15 +4317,14 @@
 
 void ClassLinker::ResolveMethodExceptionHandlerTypes(ArtMethod* method) {
   // similar to DexVerifier::ScanTryCatchBlocks and dex2oat's ResolveExceptionsForMethod.
-  const DexFile::CodeItem* code_item =
-      method->GetDexFile()->GetCodeItem(method->GetCodeItemOffset());
-  if (code_item == nullptr) {
+  CodeItemDataAccessor accessor(method);
+  if (!accessor.HasCodeItem()) {
     return;  // native or abstract method
   }
-  if (code_item->tries_size_ == 0) {
+  if (accessor.TriesSize() == 0) {
     return;  // nothing to process
   }
-  const uint8_t* handlers_ptr = DexFile::GetCatchHandlerData(*code_item, 0);
+  const uint8_t* handlers_ptr = accessor.GetCatchHandlerData(0);
   uint32_t handlers_size = DecodeUnsignedLeb128(&handlers_ptr);
   for (uint32_t idx = 0; idx < handlers_size; idx++) {
     CatchHandlerIterator iterator(handlers_ptr);