Move Breeze to Framework

[Carl Schwan]

Hi,

Considering that all of our apps are relying on breeze and on platform outside of Plasma, this is even a
required dependency, I think breeze should be a tier 3 framework and not be part of Plasma. The idea
is not new and this was on the KF6 board: https://phabricator.kde.org/T12611

There are some advantages:

- Ensuring that styling changes in Breeze, Kirigami and qqc2-desktop-style are synchronized as they are on
the same release cycle
- Don't have apps depend on a Plasma component when compiled for Windows and macOS
- Apps can now rely on some new behavior of breeze with either depending a specific minimum version of
framework or using ifdefs

There is also a few issues first which need to be resolved first:

- Licensing: Breeze is GPL but framework is LGPL. Honestly I would just ignore it and make it clear in the
repo that Breeze is an exception to the LGPL rule, so that no one use it under the wrong license by mistake
- Not everything in the breeze repo belong to framework. Notably:
    - Wallpapers: probably should be plasma-workspace as they are used by both plasma mobile and plasma
      desktop.
    - Window decoration: probably should be moved to KDecoration so that the KDecoration provides also a
      default style. Seeing how the past few merge requests regarding the window decoration in breeze were
      closely linked to other changes in KDecoration. This probably would make sense even if we end up keeping
      breeze in plasma.
    - Colors: these were already moved to KColorScheme, so we could remove the duplication one way or the
      other.

Cheers,
Carl