feat(code chunk outputs): add a stencila-ui-node-outputs component and components for common output types e.g. stencila-string, stencila-image-object etc

[nokome]

Summary

Problem

The <stencila-code-chunk> component needs a UI component to display its outputs. This is current unimplemented:

Currently, the designs for this are component are minimal and don't show how to display the actual outputs:

The outputs of a code chunk can be any Node type but will usually be a primitive type (as listed in "Data values" in #2027), an ImageObject (e.g. a plot) or a Datatable (tabular data with columns having specific types).

The examples/kernels/code-chunk/output-types-r.json and examples/kernels/code-chunk/output-types-python.json have examples of all these output types and illustrate how display of outputs need to be improved.

Each output node needs to be presented separately

This is actually six separate primitive outputs from the one CodeChunk but they are all on the same line:

Datatables are not displaying at all because on how they are encoded to DOM HTML

Images are shown at full size and not constrained to be within the node card

Tasks

• implement a collapsible <stencila-ui-node-outputs> component (similar to stencila-ui-node-messages and stencila-ui-node-authors)
• implement components for common node types found in code chunk outputs:
  • Primitive node types
    • Boolean
    • Integer
    • UnsignedInteger
    • Number
    • String
    • Array
    • Object
  • ImageObject
  • DataTable