platform_impl/linux/x11: fix deadlock in fn set_fullscreen_inner

[BurtonQin]

This is a double-lock bug in windows.rs:
The first lock is at L641 in set_fullscreen_inner():

winit/src/platform_impl/linux/x11/window.rs

Lines 641 to 643 in 03335ce

	let mut shared_state_lock = self.shared_state.lock();
	if let Some(position) = shared_state_lock.restore_position.take() {
	self.set_position_inner(position.0, position.1).queue();

Then set_position_inner() is called, where the second lock is at L988

winit/src/platform_impl/linux/x11/window.rs

Lines 984 to 988 in 03335ce

	pub(crate) fn set_position_inner(&self, mut x: i32, mut y: i32) -> util::Flusher<'_> {
	// There are a few WMs that set client area position rather than window position, so
	// we'll translate for consistency.
	if util::wm_name_is_one_of(&["Enlightenment", "FVWM"]) {
	let extents = (*self.shared_state.lock()).frame_extents.clone();

The patch drops the MutexGuard before calling set_position_inner() in set_fullscreen_inner().

[kchibisov]

Could you add a changelog entry mentioning this fix on X11?

[BurtonQin]

Sure.