message: Make "when" clauses work for extension blocks
diff: @@ -719,6 +719,8 @@ export class ExtensionManager implements InternalTypes.ExtensionManager {
  const block = state.activeBlockFrame.getBlock();
  if (block instanceof TerminalBlock) {
  whenVariables.blockType = ExtensionApi.TerminalOutputType;
  + } else if (block instanceof ExtensionBlockImpl) {
  + whenVariables.blockType = block.getBlockTypeName();
  }
  }
  