Break out plotting to own crate egui_plot (#3282)

This replaces `egui::plot` with the new crate `egui_plot`

crates/egui_plot/src/memory.rs

@@ -0,0 +1,33 @@
+use epaint::Pos2;
+
+use crate::{Context, Id};
+
+use super::{transform::ScreenTransform, AxisBools};
+
+/// Information about the plot that has to persist between frames.
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[derive(Clone)]
+pub(super) struct PlotMemory {
+    /// Indicates if the user has modified the bounds, for example by moving or zooming,
+    /// or if the bounds should be calculated based by included point or auto bounds.
+    pub(super) bounds_modified: AxisBools,
+
+    pub(super) hovered_entry: Option<String>,
+
+    pub(super) hidden_items: ahash::HashSet<String>,
+
+    pub(super) last_screen_transform: ScreenTransform,
+
+    /// Allows to remember the first click position when performing a boxed zoom
+    pub(super) last_click_pos_for_zoom: Option<Pos2>,
+}
+
+impl PlotMemory {
+    pub fn load(ctx: &Context, id: Id) -> Option<Self> {
+        ctx.data().get_persisted(id)
+    }
+
+    pub fn store(self, ctx: &Context, id: Id) {
+        ctx.data().insert_persisted(id, self);
+    }
+}