WIP: Implement the keyboard shortcuts inhibitor protocol

[NDagestad]

There are a few things still to do:

• The inhibitor key acts like a toggle switch; you pressed it to toggle between inhibited and not inhibited
  • A behaviour like qemu or virtualbox where pressing the key only give you inputs back for 1 keypress seems more intuitive
• There is no way of knowing if the input is inhibited or not
  • some kind of indicator like updating the window title would help in that regard
• Making this magic key configurable is kinda important imo
• I wanted to use a modifier with the key but it's my first time using libxkbcommon, so I haven't figured that out yet 🙃

Also, keep in mind I have not implemented a wayland protocol before, so I did my best to follow what I thought the protocol said, and as it is quite a simple one, I hope I didn't screw it up to bad.

[NDagestad]

Here's a version where the inhibitor is put in a structure, the remaining things to do listed in my initial message are still not implemented yet, I'll see if I can get to do some of theme over the weekend

[NDagestad]

Sorry for the long delay I did not expect to have so little time to work on this. It turns out that this is not the right protocol to implement, I should have used the keyboard_shortcuts_inhibit_unstabe protocol instead which has the benefit of not being wlroots specific This update is not handling seats correctly so multi seat setups will not work. I saw you are capping the line length as 80, I tried to stay close to that but a few lines are a little longer.