Refreshes the copy of Dialecto's overlay that live mode serves from the
site's own origin (priv/static/overlay.js). For maintainers of this
package: build the overlay in the Dialecto repository first
(mix esbuild in_context), then run
mix dialecto_in_context.refresh_overlay [--from PATH]PATH defaults to ../../priv/static/assets/in-context/overlay.js, where
the Dialecto repository puts it relative to this package. A test in the
Dialecto repository fails when the copy differs from a fresh build.