Cockpit's javascript debuginfo map files

[Stef Walter]

ignatenkobrain asked on #cockpit to describe our requirements around
javascript debuginfo so those can be taken into account in efforts such as:

https://fedoraproject.org/wiki/Changes/ParallelInstallableDebuginfo

Here they are:

* Cockpit is written mostly in javascript.

* This javascript runs in the browser. The browser may not be
   a Linux system. This means Cockpit code as installed in Fedora
   Debian or Ubuntu is actually running on a Mac, Windows, or Linux.

* Browsers load .map files that live next to the javascript .js
   files which are loaded. They make an HTTP request for this data.

* Cockpit assets loadable by the browser are placed in
   /usr/share/cockpit/<package>/ directories

This is documented here:
   http://cockpit-project.org/guide/latest/packages.html

* The map files should be available for loading into the web browser
   when cockpit-debuginfo is installed in order to provide assistance in
   debugging Cockpit.

* The map files are not architecture specific, but are tightly bound
   to the Cockpit javascript that is installed.

* The map files are produced by a myriad of technologies. In Cockpit's
   case these are 'webpack', 'uglify-js' and 'less'. These technologies
   change rapidly over time, as does much about javascript :S

* There are also map files for stylesheets and other loadable
   assets on the page. These non-javascript debuginfo should be
   handled in the same way.

More info:
https://www.html5rocks.com/en/tutorials/developertools/sourcemaps/

File format:
https://www.html5rocks.com/en/tutorials/developertools/sourcemaps/

Hope that helps,

Stef