X11: move dock window out of bounds when hidden

[lenemter]

Fixes #2101

This is very very bad code but I just couldn't find other solution. So far I tried:

• Minimizing window
• Using _NET_WM_STATE_HIDDEN (which is basically minimizing AFAIK)
• Blocking X11 window events by changing its event mask
• Using XShape extension

Nothing worked. If you know any other solution please let me know.

[leolost2605]

Tbh I think at some point we should just stop doing workarounds and instead go back to shipping plank for X since the whole infrastructure here (i.e. the new dock, the protocol, everything in /ShellClients) was never intended, tested or designed to work with X11 and just retrofitted into it with hopes it will work.
And IMHO this whole thing just gets messier and messier and therefore hard to maintain since always two scenarios have to be tested all at the risk of reducing quality for all sessions.
I'm not saying this point should be now (although I'd like it to be) but we should at least think about it.

[lenemter]

@leolost2605 I don't agree with that. If we don't adapt gala's code to X11, the same bugs will happen with Wingpanel when we'll implement elementary/wingpanel#53 for example. And suddenly we need to ship two versions of the same component

[leolost2605]

Something like elementary/wingpanel#53 would be pretty much the only reason to support this on X and I think it's not worth polluting the codebase for that. Since there also doesn't seem to be a lot of movement regarding it I don't see it as a valid argument right now.
And even if something like elementary/wingpanel#53 would be agreed upon I'd argue that it can land in Wayland only because X11 can be considered deprecated and can hopefully be completely dropped very soon.
I don't think it's worth supporting it at the cost of a messy codebase especially since afaik apart from very specific edge cases Wayland provides a better experience as of today (tbh I also don't quite get why X is still the default for OS8).