Display Visible History on timeline when the mouse hovers the UI (#4259)

### What

- Fixes #4141

<img width="1791" alt="image"
src="https://github.com/rerun-io/rerun/assets/49431240/049217b0-2a2b-4204-9394-465045c484e4">
<img width="1835" alt="image"
src="https://github.com/rerun-io/rerun/assets/49431240/4faf657a-4497-46b4-bad8-dbac4660bc09">


### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested [demo.rerun.io](https://demo.rerun.io/pr/4259) (if
applicable)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG

- [PR Build Summary](https://build.rerun.io/pr/4259)
- [Docs
preview](https://rerun.io/preview/8134b6de51524b7df3556157a202f607c3f3ed63/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/8134b6de51524b7df3556157a202f607c3f3ed63/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

crates/re_time_panel/src/lib.rs

@@ -266,6 +266,8 @@ impl TimePanel {
         let time_bg_area_painter = ui.painter().with_clip_rect(time_bg_area_rect);
         let time_area_painter = ui.painter().with_clip_rect(time_fg_area_rect);
 
+        paint_visible_history_range(&self.time_ranges_ui, ctx, ui.painter(), time_fg_area_rect);
+
         ui.painter().hline(
             0.0..=ui.max_rect().right(),
             timeline_rect.bottom(),
@@ -742,6 +744,9 @@ fn collapsed_time_marker_and_time(ui: &mut egui::Ui, ctx: &mut ViewerContext<'_>
             time_ranges_ui.snap_time_control(ctx);
 
             let painter = ui.painter_at(time_range_rect.expand(4.0));
+
+            paint_visible_history_range(&time_ranges_ui, ctx, &painter, time_range_rect);
+
             painter.hline(
                 time_range_rect.x_range(),
                 time_range_rect.center().y,
@@ -763,6 +768,30 @@ fn collapsed_time_marker_and_time(ui: &mut egui::Ui, ctx: &mut ViewerContext<'_>
     current_time_ui(ctx, ui);
 }
 
+fn paint_visible_history_range(
+    time_ranges_ui: &TimeRangesUi,
+    ctx: &mut ViewerContext<'_>,
+    painter: &egui::Painter,
+    rect: Rect,
+) {
+    if let Some(time_range) = ctx.rec_cfg.visible_history_highlight {
+        let x_from = time_ranges_ui.x_from_time_f32(time_range.min.into());
+        let x_to = time_ranges_ui.x_from_time_f32(time_range.max.into());
+
+        if let (Some(x_from), Some(x_to)) = (x_from, x_to) {
+            let visible_history_area_rect =
+                Rect::from_x_y_ranges(x_from..=x_to, rect.y_range()).intersect(rect);
+
+            painter.rect(
+                visible_history_area_rect,
+                0.0,
+                egui::Color32::WHITE.gamma_multiply(0.1),
+                egui::Stroke::NONE,
+            );
+        }
+    }
+}
+
 fn help_button(ui: &mut egui::Ui) {
     // TODO(andreas): Nicer help text like on space views.
     re_ui::help_hover_button(ui).on_hover_text(

crates/re_viewer/src/ui/selection_panel.rs

@@ -48,6 +48,9 @@ impl SelectionPanel {
                 ..Default::default()
             });
 
+        // Always reset the VH highlight, and let the UI re-set it if needed.
+        ctx.rec_cfg.visible_history_highlight = None;
+
         panel.show_animated_inside(ui, expanded, |ui: &mut egui::Ui| {
             // Set the clip rectangle to the panel for the benefit of nested, "full span" widgets
             // like large collapsing headers. Here, no need to extend `ui.max_rect()` as the