X11: Fix window position setting ignored when fullscreen

[murarth]

When Window::set_outer_position is called while a window is fullscreen,
the given position will be saved and will be assigned to the window when
it leaves fullscreen mode.

This addresses one of the issues described in #978.

• Tested on all platforms changed
• Compilation warnings were addressed
• cargo fmt has been run on this branch
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

[Osspial]

I tested set_outer_position on Windows when fullscreened, and we get similarly nonsensical behavior there. I feel like we should standardize and document the behavior of window position/size manipulation functions on fullscreen windows across platforms, to avoid gotchyas when developers are only regularly testing one platform.

Is there any reason set_outer_position and set_inner_size shouldn't just return hard errors when the window is in fullscreen mode? I don't think overloading set_outer_position as set_restore_position when the window is fullscreened is a good idea.

[murarth]

Is there any reason set_outer_position and set_inner_size shouldn't just return hard errors when the window is in fullscreen mode? I don't think overloading set_outer_position as set_restore_position when the window is fullscreened is a good idea.

cc @chrisduerr, author of the original issue

[chrisduerr]

Doesn't seem to help for me. Window is still spawned on incorrect monitor and it still has the incorrect size after unfullscreening.

[murarth]

Ah, right. The issue was that setting position at startup was ignored, which has a different root cause. I will close this PR and approach the issue from a different angle.