Remove mterp reliance on code item layout

Pass dex instruction pointer intead of code item pointer to the mterp
entry code. This removes a dependency on the code item layout since it
may change in the future for compact dex.

Bug: 63756964
Test: test/testrunner/testrunner.py --host -j40

Change-Id: Icfffb2e17372439f0833ecce1c0ddb05e7e7e69c
diff --git a/runtime/interpreter/interpreter_mterp_impl.h b/runtime/interpreter/interpreter_mterp_impl.h
index 1be20fa..7aa5a34 100644
--- a/runtime/interpreter/interpreter_mterp_impl.h
+++ b/runtime/interpreter/interpreter_mterp_impl.h
@@ -32,7 +32,7 @@
 
 // Mterp does not support transactions or access check, thus no templated versions.
 extern "C" bool ExecuteMterpImpl(Thread* self,
-                                 const DexFile::CodeItem* code_item,
+                                 const uint16_t* dex_instructions,
                                  ShadowFrame* shadow_frame,
                                  JValue* result_register) REQUIRES_SHARED(Locks::mutator_lock_);