Implement MotionRuntime.interactions() API

library/src/main/java/com/google/android/material/motion/MotionRuntime.java

@@ -31,6 +31,7 @@ public final class MotionRuntime {
 
   private final List<Subscription> subscriptions = new ArrayList<>();
   private final SimpleArrayMap<View, ReactiveView> cachedReactiveViews = new SimpleArrayMap<>();
+  private final SimpleArrayMap<Object, List<Interaction>> cachedInteractions = new SimpleArrayMap<>();
 
   /**
    * Subscribes to the stream, writes its output to the given property, and observes its state.
@@ -62,6 +63,13 @@ public final <O, T> void addInteraction(
   public final <O, T> void addInteraction(
     Interaction<O, T> interaction, O target, ConstraintApplicator<T> constraints) {
     interaction.apply(this, target, constraints);
+    List<Interaction> interactions = cachedInteractions.get(target);
+    if (interactions == null) {
+      interactions = new ArrayList<>();
+      cachedInteractions.put(target, interactions);
+    }
+
+    interactions.add(interaction);
   }
 
   /**
@@ -76,4 +84,15 @@ public ReactiveView get(View view) {
 
     return reactiveView;
   }
+
+  public <I extends Interaction> List<I> interactions(View view, Class<I> klass) {
+    List<Interaction> interactions = cachedInteractions.get(view);
+    List<I> filteredInteractions = new ArrayList<>();
+
+    for (Interaction i: interactions) {
+      if(klass.isInstance(i))
+        filteredInteractions.add((I)i);
+    }
+    return filteredInteractions;
+  }
 }