Implement <Composer> and <BasicWebChat> instead of <ReactWebChat> from BotFramework WebChat

>`` is the conventional entrypoint for the chat experience. In fact, [](https://github.com/microsoft/BotFramework-WebChat/blob/master/packages/component/src/ReactWebChat.js) is a React component comprised from two components:

>[``](https://github.com/microsoft/BotFramework-WebChat/blob/master/packages/component/src/Composer.js) is the API container. It is designed to be platform-neutral and enables Web Chat APIs for its descendants;
[``](https://github.com/microsoft/BotFramework-WebChat/blob/master/packages/component/src/BasicWebChat.js) is the conventional UI component. It consumes Web Chat APIs and render using HTML.
To enable composition mode, `` will be replaced by `` and ``. All props previously passed to `` will be passed to `` instead.

Example from: https://github.com/microsoft/BotFramework-WebChat/tree/main/samples/04.api/m.enable-composition-mode#enable-composition-mode

Would be good to use the bare elements, so we can use the API hooks.

Start with the BotFramework WebChat Composer and BasicWebChat references in the issue, then compare them with the current ReactWebChat usage in this repository. Use the linked composition-mode sample as the expected integration shape; done means the chat uses the bare components and API hooks while preserving the existing experience.

Written by the indexing model from the issue text.