Functions for checking pkgdown.yaml without building

[gravesti]

Hi pkgdown team, I'm looking at implementing a pre-commit git hook for our developers to make sure that they have updated the pkgdown.yaml so we can avoid those Topics missing from index: my_new_function errors on the later checks.
It looks like this could be mostly achieved with

build_reference_index()
build_articles_index()

However to make it a bit faster and to avoid having to have Pandoc available in the pre-commit environment, I'm wondering if it would be possible to have this functionality but without the call to render_page()?
Or maybe it would be enough to export data_reference_index and data_articles_index?