fix: public api surface fixes + stability markers

- ts-api-guardian will now error if a new public symbol is added with a stability marker (`@stable`, `@experimental`, `@deprecated`)
- DomEventsPlugin and KeyEventsPlugin were removed from public api surface - these classes is an implementation detail
- deprecated BROWSER_PROVIDERS was removed completely
- `@angular/compiler` was removed from the ts-api-guardian check since this package shouldn't contain anything that users need to directly import
- the rest of the api surface was conservatively marked as stable or experimental

BREAKING CHANGES: DomEventsPlugin and KeyEventsPlugin previously exported from core are no longer public - these classes are implementation detail.

Previously deprecated BROWSER_PROVIDERS was completely removed from platform-browser.

Closes #9236
Closes #9235
Ref #9234

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

@@ -25,14 +25,18 @@ export interface IterableDiffer {
 }
 
 /**
-  * An optional function passed into {@link NgFor} that defines how to track
-  * items in an iterable (e.g. by index or id)
+ * An optional function passed into {@link NgFor} that defines how to track
+ * items in an iterable (e.g. by index or id)
+ *
+ * @stable
  */
 export interface TrackByFn { (index: number, item: any): any; }
 
 
 /**
  * Provides a factory for {@link IterableDiffer}.
+ *
+ * @stable
  */
 export interface IterableDifferFactory {
   supports(objects: any): boolean;

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

@@ -15,6 +15,8 @@ import {ChangeDetectorRef} from '../change_detector_ref';
 
 /**
  * A differ that tracks changes made to an object over time.
+ *
+ * @stable
  */
 export interface KeyValueDiffer {
   diff(object: any): any /** TODO #9100 */;
@@ -23,6 +25,8 @@ export interface KeyValueDiffer {
 
 /**
  * Provides a factory for {@link KeyValueDiffer}.
+ *
+ * @stable
  */
 export interface KeyValueDifferFactory {
   supports(objects: any): boolean;

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

@@ -33,5 +33,6 @@
  *
  * Invoking `{{ 'ok' | repeat:3 }}` in a template produces `okokok`.
  *
+ * @stable
  */
 export interface PipeTransform { transform(value: any, ...args: any[]): any; }