Applying optional setup configuration files allows developers to modify
the Demo editor environment via Hooks, e.g. to set custom `initialHtml`
for the editor.

The `require.context` function is undefined in the test environment, as
it is a Metro-specific capability. The most straightforward way to avoid
test failures is to disable this code that relates to the local
development workflow.

Contributors will likely never discover or benefit from this
customization ability if it is not documented.