Function run_merge_finalize 

pub(crate) fn run_merge_finalize(
    render_options: RenderOptions,
    compiler: &Compiler,
) -> Result<(), Error>

Renders and writes cross-crate info files, like the search index. This function exists so that we can run rustdoc without a crate root in the --merge=finalize mode. Cross-crate info files discovered via --read-doc-meta-dir are combined and written to the doc root.