Move arena_bit_vector.h/cc to compiler/utils.

Also move MIR's BasicBlock related code from arena_bit_vector.h to
bit_vector_block_iterator.cc.

Change-Id: I85c224b387d31cf57a1ef1f1a36eaadf22f1c85d
diff --git a/compiler/dex/ssa_transformation.cc b/compiler/dex/ssa_transformation.cc
index 0f79f41..4e258ef 100644
--- a/compiler/dex/ssa_transformation.cc
+++ b/compiler/dex/ssa_transformation.cc
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include "bit_vector_block_iterator.h"
 #include "compiler_internals.h"
 #include "dataflow_iterator-inl.h"
 
@@ -248,9 +249,9 @@
   }
 
   /* Calculate DF_up */
-  ArenaBitVector::BasicBlockIterator it(bb->i_dominated, cu_);
+  BitVectorBlockIterator it(bb->i_dominated, cu_);
   for (BasicBlock *dominated_bb = it.Next(); dominated_bb != nullptr; dominated_bb = it.Next()) {
-    ArenaBitVector::BasicBlockIterator inner_it(dominated_bb->dom_frontier, cu_);
+    BitVectorBlockIterator inner_it(dominated_bb->dom_frontier, cu_);
     for (BasicBlock *df_up_block = inner_it.Next(); df_up_block != nullptr;
          df_up_block = inner_it.Next()) {
       CheckForDominanceFrontier(bb, df_up_block);