Move the filter bar and the timeline onto the library's Slint global

The date-range fields and their band on the capture-time axis, the
timeline's bars, labels, scrub/pinch/pan/zoom callbacks and its
sweep/current-bucket/anchored state, and the filter bar's people chips,
mode, eyes-open toggle and gesture reference move from AppWindow onto the
`Library` global. Rust reaches them through window.global::<Library>()
rather than window.set_/get_/on_ on the root, as the earlier commits on
this branch did for the grid's cells, selection, ratings and keywords.

ui/dr-ui/src/library_ui/window.rs

@@ -254,7 +254,7 @@ pub(super) fn load_window(window: &AppWindow, ctl: &Rc<LibraryController>) {
     let window_size = *ctl.window.borrow();
     let offset = (*ctl.offset.borrow()).min(total.saturating_sub(window_size.min(total)));
     *ctl.offset.borrow_mut() = offset;
-    window.set_library_offset(offset as i32);
+    window.global::<Library>().set_library_offset(offset as i32);
 
     // The axis the scrubber draws. A `MIN`/`MAX` and a `GROUP BY` over the
     // whole scope — 5.7 ms on 24,000 images — and the bars do not change as the
@@ -308,7 +308,7 @@ pub(super) fn load_window(window: &AppWindow, ctl: &Rc<LibraryController>) {
                 Some((lo, hi)) => (lo.min(t), hi.max(t)),
             })
         });
-    window.set_library_window_label(
+    window.global::<Library>().set_library_window_label(
         match span {
             Some((lo, hi)) => format!("{} – {}", format_date(lo), format_date(hi)),
             // Nothing here has a date yet: EXIF is read as thumbnails load, so