feat(core/linker): add SimpleChanges type to lifecycle_hooks to simplify OnChanges signature

Closes #8557

modules/@angular/core/src/change_detection.ts

@@ -11,6 +11,7 @@ export {
 
   WrappedValue,
   SimpleChange,
+  SimpleChanges,
   PipeTransform,
   DefaultIterableDiffer,
   IterableDiffers,

modules/@angular/core/src/change_detection/change_detection.ts

@@ -41,6 +41,7 @@ export {
   looseIdentical,
   uninitialized
 } from './change_detection_util';
+export {SimpleChanges} from '../metadata/lifecycle_hooks';
 
 /**
  * Structural diffing for `Object`s and `Map`s.

modules/@angular/core/src/metadata/lifecycle_hooks.ts

@@ -11,6 +11,15 @@ export enum LifecycleHooks {
   AfterViewChecked
 }
 
+/**
+ * A `changes` object whose keys are property names and
+ * values are instances of {@link SimpleChange}. See {@link OnChanges}
+ */
+export interface SimpleChanges {[propName: string]: SimpleChange};
+
+/**
+ * @internal
+ */
 export var LIFECYCLE_HOOKS_VALUES = [
   LifecycleHooks.OnInit,
   LifecycleHooks.OnDestroy,
@@ -53,7 +62,7 @@ export var LIFECYCLE_HOOKS_VALUES = [
  * class MyComponent implements OnChanges {
  *   @Input() myProp: any;
  *
- *   ngOnChanges(changes: {[propName: string]: SimpleChange}) {
+ *   ngOnChanges(changes: SimpleChanges) {
  *     console.log('ngOnChanges - myProp = ' + changes['myProp'].currentValue);
  *   }
  * }
@@ -72,7 +81,7 @@ export var LIFECYCLE_HOOKS_VALUES = [
  * bootstrap(App).catch(err => console.error(err));
  * ```
  */
-export abstract class OnChanges { abstract ngOnChanges(changes: {[key: string]: SimpleChange}); }
+export abstract class OnChanges { abstract ngOnChanges(changes: SimpleChanges); }
 
 /**
  * Implement this interface to execute custom initialization logic after your directive's