replace qmldir with JSON

This was discussed in August 2013:

https://lists.qt-project.org/pipermail/development/2013-August/024821.html

the link will break later, no doubt, but the thread was Re: qml, qrc and deployment. In the context of getting rid of qmlbundle (which we did, see QTBUG-27783):

On 13 Aug 2013, at 12:40, Thomas Hartmann <Thomas.Hartmann@digia.com> wrote:

Another topic that came up was qmldir. Since Qt 5 now supports to .json

to describe and annotate a plugin, shouldn't we use this instead of

another arbitrary file format? Of course we will continue support for

qmldir, but we should depreciate it and use .json instead. Like for any

other plugin in Qt.

The qmldir file could be replaced by qmldir.json in the pure .qml plugin

case.

If the plugin is converted to .rcc the .rcc file contains the

qmldir.json file.

I'm not sure if it has to be called qmldir.json, but some sort of JSON file will have more structure than the ad-hoc format that we have now. And there are precedents, such as that we use JSON for annotating plugins. So I guess we should try to be consistent with that somehow: maybe consider that json file to extend the plugin's annotation?

I would even more like to be able to operate without qmldir files at all, at least sometimes. It should be possible to deploy a plugin as a single file, if the resources include all the bundled QML, and the annotation tells the engine enough about what to do with it.