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/compiler/driver/compiler_driver.cc b/compiler/driver/compiler_driver.cc
index 0631c0f..68f963e 100644
--- a/compiler/driver/compiler_driver.cc
+++ b/compiler/driver/compiler_driver.cc
@@ -949,14 +949,14 @@
       ArtMethod* method,
       std::set<std::pair<dex::TypeIndex, const DexFile*>>* exceptions_to_resolve)
       REQUIRES_SHARED(Locks::mutator_lock_) {
-    const DexFile::CodeItem* code_item = method->GetCodeItem();
-    if (code_item == nullptr) {
+    if (method->GetCodeItem() == nullptr) {
       return;  // native or abstract method
     }
-    if (code_item->tries_size_ == 0) {
+    CodeItemDataAccessor accessor(method);
+    if (accessor.TriesSize() == 0) {
       return;  // nothing to process
     }
-    const uint8_t* encoded_catch_handler_list = DexFile::GetCatchHandlerData(*code_item, 0);
+    const uint8_t* encoded_catch_handler_list = accessor.GetCatchHandlerData();
     size_t num_encoded_catch_handlers = DecodeUnsignedLeb128(&encoded_catch_handler_list);
     for (size_t i = 0; i < num_encoded_catch_handlers; i++) {
       int32_t encoded_catch_handler_size = DecodeSignedLeb128(&encoded_catch_handler_list);