Plot::Items::default_visible allow hidden on init

[haricot]

added feature described in this issue #2395

[emilk]

Suggested change

	let hiddened= !(checked && visible || !checked && !visible);
	if hiddened {
	if checked != visible {

[emilk]

…though I struggle to follow he logic

[haricot]

another possible logic without default_visible but with visible checking if it's in hidden_items.
(requires a PR to access hidden items, which seems necessary to know if the item is hidden in a future case.
and surely a specific logic for the visible.)

let visibility_points = !hidden_items.contains("Points");
plot_ui.points(points.name("Points").visible(visibility_points);

although with default_visible we set a state from the start, we don't have access to its modified state.
while with visible it will allow to have its state hidden or not dynamically.

I don't think they are the same thing all the same.
with default_visible we define a state from the start which is clear to me.
When to know if it is in hidden_items it is another problem.
I think I have a preference for default_visible to solve this feature.
But maybe an alternative and necessary PR to compare.

[emilk]

egui_plot has recently been moved to its own repository, at https://github.com/emilk/egui_plot

This will hopefully speed up its development by having more reviewers and maintainers.

Please re-open this PR at https://github.com/emilk/egui_plot/pulls

See also:

• Looking for maintainer egui_plot#58
• Move egui_plot to its own repo #4828