Show variables in the debug panel

[jtpio]

For the implementation, reusing the conponent from @jupyterlab/json-extension could be a good starting point: https://github.com/jupyterlab/jupyterlab/blob/75166c60cd0d0c74045b66de473be6ca39c94a7c/packages/json-extension/src/component.tsx#L33

Another option is to use the react-inspector package: https://github.com/storybookjs/react-inspector

As a reference, this is what it looks like in VS Code:

[jtpio]

Simple prototype implemented in: #5 (comment).

A more elaborate UI will be developed in https://github.com/jupyterlab/debugger