Generate links to index.html #4258

The generated link to a library has the form <a href="ascii/">ascii</a>.

That makes it hard to examine the generated docs locally, because the browser will open the local .../ascii/ directory, not the .../ascii/index.html file that a web server would (presumably) redirect to or send instead when you ask for the URI .../ascii/.

If the link had been <a href="ascii/index.html">ascii</a>, you could browser generated docs directly from disk.

The current behavior is deliberate. From lib/src/model/library.dart:

    // The file name for a library is 'index.html', so we just link to the
    // directory name. This keeps the URL looking short, _without_ the
    // 'index.html' in the URL.
    return '${package.baseHref}$dirName/';

That works when generating HTML for a web server. If the URL being short in that case is more important than making it easily locally readable, then the current behavior is what we want.

(Unless we can have a flag to choose? As a package author, I want to check how my docs look before publishing. That's less convenient with the current behavior. Or we could have a dart doc server command which generates the docs, then serves them as a HTTP server on a local port.)