[lib][native][web] Add support for rendering array of messages in RobotextChatMessageInfoItem

Summary:
This diff makes it possible to render a robotext that corresponds to a list of messages.

We don't actually render a list of messages anywhere yet.

Depends on D13685

Test Plan: Tested in combination with the following diffs, where I construct RobotextChatMessageInfoItem with an array of messageInfos to represent combined messages (ENG-9559)

Reviewers: tomek

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D13686