Move ratings, flags and keywording onto the library's Slint global

The keywording sheet's rows and its open/assign/unassign callbacks, the
star and flag callbacks a cell click or a judgement key fires, the burst
toggle and representative-chosen callbacks, the trash-selection shortcut,
and the rating/unjudged/flag filter chips with their rating-counts model
move from AppWindow onto the `Library` global started in the previous
commit. Rust reaches them through window.global::<Library>() rather than
window.set_/get_/on_ on the root.

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

@@ -883,17 +883,23 @@ enum Found {
 /// first act would be to try to clear a filter the bar says is off.
 fn push_filter(window: &AppWindow, ctl: &Rc<LibraryController>) {
     let filter = ctl.filter.borrow().clone();
-    window.set_library_filter_min_rating(filter.min_rating as i32);
-    window.set_library_filter_unjudged(filter.unjudged);
+    window
+        .global::<Library>()
+        .set_library_filter_min_rating(filter.min_rating as i32);
+    window
+        .global::<Library>()
+        .set_library_filter_unjudged(filter.unjudged);
     // The bar's own numbering, from `on_library_filter_flag_changed`. It has no
     // code for `Unflagged` because it cannot produce one — "nothing has judged
     // this" is the `unjudged` chip, over both stars and flags — so a place can
     // never carry one either, and it falls in with "no flag constraint".
-    window.set_library_filter_flag(match filter.flag {
-        Some(dr_types::FlagState::Pick) => 1,
-        Some(dr_types::FlagState::Reject) => 2,
-        _ => 0,
-    });
+    window
+        .global::<Library>()
+        .set_library_filter_flag(match filter.flag {
+            Some(dr_types::FlagState::Pick) => 1,
+            Some(dr_types::FlagState::Reject) => 2,
+            _ => 0,
+        });
     window
         .global::<Library>()
         .set_library_local_only(filter.local_only);