Create Behat meta tags for subsystems and plugins

I wonder whether we should provide a way to create some meta tags for behat for some areas, for example we have the core_question subsystem whose documented location is "question". We also have plugin types:

• qtype in question/type
• qbehaviour in question/behaviour
• qformat in question/format

It would be relatively easy to check through the list of plugintypes and subsplugins for the subsystem location and look for those in a subdirectory. So we could create a meta tag for @meta:core_question which runs core_question and any tags relating to the plugintypes in the question directory, and any plugins and subplugins of that too.

The same can apply to areas such as mod_assign (which has subplugins) so that if you run @meta:mod_assign it will run @mod_assign, and any of the subplugins for assign.

This would require some upstream changes to Behat, or possibly even Gherkin, depending on how it was implemented.