Steps to reproduce the issue

Create a module that uses the new module dispatcher (#19834). With the following file structure:

Dispatcher
    Dispatcher.php
services
    provider.php
tmpl
    default.php

Try to install it.

Expected result

Module installed.

Actual result

Installation fails with errors:

Module Install: No module file specified.
Error installing module

System information (as much as possible)

4.0-dev

Additional comments

Installer expects mod_whatever.php file to be present and defined in the manifest file.