Function merge_rustdoc_cci 

fn merge_rustdoc_cci(
    builder: &Builder<'_>,
    build_compiler: Compiler,
    json_files: &[PathBuf],
    out_dir: &Path,
)

Run rustdoc to merge cross-crate info metadata (like the search index) from individual executions of rustdoc into out_dir. The json_files parameter should contain paths to JSON file artifacts generated by previous executions of cargo doc.