qt_attributions.json files should be valid JSON

The qt_attributions.json files are currently invalid JSON, because of entries like this:

    "Copyright": "Copyright (c) 1995-2022 The PNG Reference Library Authors
Copyright (c) 2000-2022 Cosmin Truta
...
Copyright (c) 1995-1996 Tim Wegner"

The newlines must be replaced by \n or the Copyright field should be allowed to be an array of strings.

Patch that goes the \n route: https://codereview.qt-project.org/c/qt/qtbase/+/308531

However, it turns out that this results in quite unreadable, overly long string literals.

Let's do it like this:

• change QUIP 007 and state that the Copyright field allows string or string[].
• change qtattributionsscanner to accept string arrays. The array is joined to a single string with newlines.
• bulk-change the qt_attribution.json files