iris: move text state into shared resources

core/src/util/slot.rs

@@ -71,6 +71,10 @@ impl<T> SlotVec<T> {
     pub fn is_empty(&self) -> bool {
         self.len() == 0
     }
+
+    pub fn values_mut(&mut self) -> impl Iterator<Item = &mut T> {
+        self.data.iter_mut().filter_map(|(_, value)| value.as_mut())
+    }
 }
 
 impl<T> Default for SlotVec<T> {