message: Make RMUI handle multiple case keys
  Summary: `d8` generates switch statements with multiple edges to a single case block. This diff adapts the `SwitchMap` to be able to handle case blocks with multiple incoming edges.
diff: @@ -1828,7 +1828,9 @@ void ControlFlowGraph::remove_block(Block* block) {
  }
  delete_pred_edges(block);
  delete_succ_edges(block);
  - m_blocks.erase(block->id());
  + auto num_removed = m_blocks.erase(block->id());
  + always_assert_log(num_removed == 1,
  + "Block wasn't in CFG. Attempted double delete?");
  block->m_entries.clear_and_dispose();
  delete block;
  }
  