Draft: Start making breeze-icons REUSE compliant

[Despite being marked as Draft, feel free to review]

This is part of an effort to make KDE software properly licensed according to SPDX. See the following for details:

• https://community.kde.org/Guidelines_and_HOWTOs/Licensing
• https://community.kde.org/Policies/Licensing_Policy (especially the section about icons)

This MR:

• uses licensedigger to find the licenses of existing files
• adds missing LICENSES
• adds a REUSE.toml (.reuse/dep5 is deprecated)

Since I didn't look up who should be the "Upstream-Contact" (PackageSupplier) yet, I left it as none.

Since I didn't look up how to handle the authorship of image files yet, I left it as none.

It's possible to add SPDX headings to SVG files, like in https://invent.kde.org/frameworks/breeze-icons/-/blob/master/icons/actions/16/folder-edit-sign-encrypt.svg?ref_type=heads&plain=1 (though it would be extremely painful to do so for every single file).

Todo:

• add missing readme/cmake/yaml/js files
• look into filling <year> <owner> in the BSD-3-Clause
• add reuse lint Gitlab template once the MR is done