Clear completion when switching windows via click

[the-mikedavis]

The completion component assumes that it operates on the same View but it's possible to break this assumption by switching windows through left-clicking. I believe we should clear the completion menu when switching windows to fix this.

This change fixes a panic for this scenario:

• Open a buffer with LSP completion available
• Split the window (for example <C-w>v)
• Enter insert mode and trigger the completion menu
• Select a completion candidate (for example with <C-n>)
• Switch to the original window by left-clicking in its area
• Enter insert mode and make edits (for example o<backspace>)

This will trip the assert_eq in Document::restore.

[the-mikedavis]

Ideally we would close completion on any window switch from within Editor::focus but I believe that would need the move-compositor-to-helix-view change (#5632 (comment))

[pascalkuthe]

We can merge this as is to get the panic out of tree but I actually included the same fix in #8021 :D

Sorry I confused something. This is a good catch! Not quite as good as doing it in editor::focus but realistically changing focus while a prompt is otherwise impossible anyway.

[pascalkuthe]

Ideally we would close completion on any window switch from within Editor::focus but I believe that would need the move-compositor-to-helix-view change (#5632 (comment))

That issue was about the search prompt not completion. Could we do the same there (close the current prompt)?

[the-mikedavis]

Yeah, I just mean that for both prompts and completion that we need access to the compositor from within (helix-view's) Editor to solve it really nicely as you say in #5632.

It should be possible to also close other components here:

let callback = if view_id != prev_view_id {
    self.clear_completion(editor);
    let callback: crate::compositor::Callback = Box::new(|compositor, _| {
        // Close any prompts or other components.
    });
    Some(callback)
} else {
    None
};

editor.focus(view_id);
editor.ensure_cursor_in_view(view_id);

return EventResult::Consumed(callback);

But that may need larger changes to the prompt and maybe other components. We would want to cancel whatever the prompt had selected, for example if you had :theme <sometheme> previewed and clicked another pane then it would essentially accept the preview but I would expect the prompt to cancel (PromptEvent::Abort).

I think it's possible with some more changes to the components that could be closed but it isn't quite trivial so I'd like to leave it off of this PR if possible.