Use a KWin plugin for better compatibility with Wayland

[Schneegans]

This is an attempt to get rid of the currently quite hacky approach used on KWin to get the window manager information Kando requires. Instead of a temporary KWin script, Kando now talks to a proper KWin plugin to get this information.

Pros

• This would fix the issue where the frequent loading, running, and stopping of the hacky script occasionally crashes the desktop (#855).
• This would allow opening the menu at the stylus of a tablet which is currently impossible.
• In the future there will also be a bit more window-management related stuff in Kando which I want to bring to KDE as well (like for instance activating a window during a workflow execution). Like an action which copies selected text here, switches to another window, pastes the text there. I fear that loading and stopping this script a bazillion times is a bad idea.

Cons

• Distributing a binary KWin script is not exactly easy. In many cases, people will have to compile and install it on their own.

This disadvantage makes me wonder whether it's actually worth it. It would be great if there was an easy way to install such a plugin...

The require plugin can be retrieved from here: https://github.com/kando-menu/kwin-integration

💥 Beware that this branch is already based on the upcoming Kando 3.0.0 version! So if you test this, make sure to backup your config files before as they will not be downwards compatible if you want to switch back!