code: private static ImmutableList<SoyMsgPart> buildMsgPartsForChildren(
        MsgBlockNode parent, MsgNode msgNode) {
  
      ImmutableList.Builder<SoyMsgPart> msgParts = ImmutableList.builder();
      doBuildMsgPartsForChildren(parent, msgNode, msgParts);
      return msgParts.build();
    }
docs: Builds the list of SoyMsgParts for all the children of a given parent node.
  
  @param parent Can be MsgNode, MsgPluralCaseNode, MsgPluralDefaultNode, MsgSelectCaseNode, or
  MsgSelectDefaultNode.
  @param msgNode The MsgNode containing 'parent'.