Add support for qt_attribution.json files

### Description
These are structured package-like manifests that describe many packages licensing
See https://wiki.qt.io/Qt_attribution.json and http://quips-qt-io.herokuapp.com/quip-0007.html by @kkoehne :

> qt_attribution.json files are used to document 3rd party code inside the Qt modules (from Qt 5.8 onwards). It is a JSON based format that can be processed with the licensescanner tool. It is officially documented in QUIP 7.
> A qt_attribution.json file needs to contain one JSON object, or one array of JSON objects, with the following string properties:

These are essentially similar to ABOUT files

Some examples and links:
- https://github.com/qt/qttools/tree/dev/src/qtattributionsscanner
- https://fossies.org/linux/qt-everywhere/qtbase/src/3rdparty/wasm/qt_attribution.json
- https://github.com/aedrax/pyside-setup/blob/8383c2ff7f383385707bd2fc3e33071988507910/sources/shiboken2/libshiboken/qt_attribution.json
- https://github.com/qt/qtbase/blob/dev/src/3rdparty/freebsd/qt_attribution.json