[Core] Add ParameterProvider interface.

formula/src/main/java/com/instacart/formula/ActionBuilder.kt

@@ -20,12 +20,12 @@ abstract class ActionBuilder<out Input, State>(
     /**
      * Current input associated with the Formula evaluation.
      */
-    val input: Input,
+    override val input: Input,
     /**
      * Current state associated with the Formula evaluation.
      */
-    val state: State,
-) {
+    override val state: State,
+) : ParameterProvider<Input, State> {
 
     /**
      * Adds an [Action] as part of this [Evaluation]. [Action] will be initialized

formula/src/main/java/com/instacart/formula/ParameterProvider.kt

@@ -0,0 +1,13 @@
+package com.instacart.formula
+
+interface ParameterProvider<out Input, State> {
+
+    /**
+     * Current formula input.
+     */
+    val input: Input
+    /**
+     * Current formula state.
+     */
+    val state: State
+}

formula/src/main/java/com/instacart/formula/Snapshot.kt

@@ -6,17 +6,17 @@ package com.instacart.formula
  * is a state change within the Formula hierarchy, a new snapshot will be generated and
  * [Formula.evaluate] will be called again.
  */
-interface Snapshot<out Input, State> {
+interface Snapshot<out Input, State> : ParameterProvider<Input, State> {
 
     /**
      * The current Formula input value passed by the parent.
      */
-    val input: Input
+    override val input: Input
 
     /**
      * The current Formula state value.
      */
-    val state: State
+    override val state: State
 
     /**
      * Context is a short-lived object associated with the current evaluation. It should not be

formula/src/main/java/com/instacart/formula/TransitionContext.kt

@@ -9,11 +9,11 @@ import com.instacart.formula.internal.toResult
  * Transition context provides the current [input], the current [state] and utilities to help
  * create [Transition.Result] within [Transition.toResult].
  */
-interface TransitionContext<out Input, State> {
+interface TransitionContext<out Input, State> : ParameterProvider<Input, State> {
 
     val effectDelegate: EffectDelegate
-    val input: Input
-    val state: State
+    override val input: Input
+    override val state: State
 
     /**
      * Returns a result that indicates to do nothing as part of this event.