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/optimizing/optimization.cc b/compiler/optimizing/optimization.cc
index 7149d93..d8ac696 100644
--- a/compiler/optimizing/optimization.cc
+++ b/compiler/optimizing/optimization.cc
@@ -35,6 +35,7 @@
 
 #include "bounds_check_elimination.h"
 #include "cha_guard_optimization.h"
+#include "code_item_accessors-inl.h"
 #include "code_sinking.h"
 #include "constant_folding.h"
 #include "constructor_fence_redundancy_elimination.h"
@@ -241,7 +242,8 @@
         opt = new (allocator) HDeadCodeElimination(graph, stats, name);
         break;
       case OptimizationPass::kInliner: {
-        size_t number_of_dex_registers = dex_compilation_unit.GetCodeItem()->registers_size_;
+        CodeItemDataAccessor accessor(dex_compilation_unit.GetDexFile(),
+                                      dex_compilation_unit.GetCodeItem());
         opt = new (allocator) HInliner(graph,                   // outer_graph
                                        graph,                   // outermost_graph
                                        codegen,
@@ -250,7 +252,7 @@
                                        driver,
                                        handles,
                                        stats,
-                                       number_of_dex_registers,
+                                       accessor.RegistersSize(),
                                        /* total_number_of_instructions */ 0,
                                        /* parent */ nullptr,
                                        /* depth */ 0,