Draft: [Windows] Add accesskit dependency
Goal
Enable AccessKit a11y backend to permit screenreader use.
Information
As soon as gtk4 is built with accesskit support enabled, we need to add accesskit in the environment to permit accessibility in Windows.
See #11147 (closed) for more informations and the upstream PR for msys2: https://github.com/msys2/MINGW-packages/pull/24736