message: use cfg_mutation.insert_(before/after)
  Summary:
  As in the title. Instead of inserting directly in the cfg via `find_insn`, enhance the
  use the new CFGMutation API to insert positions before and after instructions.
diff: @@ -2047,12 +2047,7 @@ static void rewrite_at_location(DexMethod* outlined_method,
  outlined_method_invocation.push_back(move_result_insn);
  }
  cfg_mutation.insert_before(first_insn_it, outlined_method_invocation);
  - cfg_mutation.flush();
  - // TODO: Instead inserting directly in the cfg via find_insn, enhance the
  - // CFGMutation class to support inserting positions before and after
  - // instructions.
  - auto dbg_pos_insertion_it = cfg.find_insn(invoke_insn, first_insn_it.block());
  std::unique_ptr<DexPosition> new_dbg_pos;
  if (call_site_pattern_ids) {
  auto manager = g_redex->get_position_pattern_switch_manager();
  @@ -2063,11 +2058,8 @@ static void rewrite_at_location(DexMethod* outlined_method,
  new_dbg_pos->bind(DexString::make_string(show(outlined_method)),
  DexString::make_string("RedexGenerated"));
  }
  - cfg.insert_before(dbg_pos_insertion_it, std::move(new_dbg_pos));
  - if (move_result_insn) {
  - dbg_pos_insertion_it =
  - cfg.find_insn(move_result_insn, first_insn_it.block());
  - }
  +
  + cfg_mutation.insert_before(first_insn_it, std::move(new_dbg_pos));
  if (last_dbg_pos) {
  new_dbg_pos = std::make_unique<DexPosition>(*last_dbg_pos);
  } else {
  @@ -2077,8 +2069,9 @@ static void rewrite_at_location(DexMethod* outlined_method,
  "[instruction sequence outliner] reverting to synthetic position in %s",
  SHOW(method));
  }
  - cfg.insert_after(dbg_pos_insertion_it, std::move(new_dbg_pos));
  -};
  + cfg_mutation.insert_after(first_insn_it, std::move(new_dbg_pos));
  + cfg_mutation.flush();
  +}
  // Manages references and assigns numeric ids to classes
  // We don't want to use more methods or types than are available, so we gather
  