add module system and move sensor into core with it

src/layout/module.rs

@@ -0,0 +1,34 @@
+use std::any::{Any, TypeId};
+
+use crate::{
+    layout::WidgetInstance,
+    util::{HashMap, Id},
+};
+
+#[allow(unused_variables)]
+pub trait UiModule: Any {
+    fn on_draw(&mut self, inst: &WidgetInstance) {}
+    fn on_undraw(&mut self, inst: &WidgetInstance) {}
+    fn on_remove(&mut self, id: &Id) {}
+}
+
+#[derive(Default)]
+pub struct Modules {
+    map: HashMap<TypeId, Box<dyn UiModule>>,
+}
+
+impl Modules {
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut (dyn UiModule + 'static)> {
+        self.map.values_mut().map(|m| m.as_mut())
+    }
+
+    pub fn get_mut<M: UiModule + Default>(&mut self) -> &mut M {
+        let rf = self
+            .map
+            .entry(TypeId::of::<M>())
+            .or_insert_with(|| Box::new(M::default()))
+            .as_mut();
+        let any: &mut dyn Any = &mut *rf;
+        any.downcast_mut().unwrap()
+    }
+}