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/platform-browser/src/dom/debug/by.ts

@@ -16,6 +16,8 @@ import {Type, isPresent} from '../../facade/lang';
 
 /**
  * Predicates for use with {@link DebugElement}'s query functions.
+ *
+ * @experimental All debugging apis are currently experimental.
  */
 export class By {
   /**

modules/@angular/platform-browser/src/dom/dom_tokens.ts

@@ -13,5 +13,7 @@ import {OpaqueToken} from '@angular/core';
  *
  * Note: Document might not be available in the Application Context when Application and Rendering
  * Contexts are not the same (e.g. when running the application into a Web Worker).
+ *
+ * @stable
  */
 export const DOCUMENT: OpaqueToken = new OpaqueToken('DocumentToken');

modules/@angular/platform-browser/src/dom/events/event_manager.ts

@@ -12,8 +12,14 @@ import {ListWrapper} from '../../facade/collection';
 import {BaseException} from '../../facade/exceptions';
 
 
+/**
+ * @stable
+ */
 export const EVENT_MANAGER_PLUGINS: OpaqueToken = new OpaqueToken('EventManagerPlugins');
 
+/**
+ * @stable
+ */
 @Injectable()
 export class EventManager {
   private _plugins: EventManagerPlugin[];

modules/@angular/platform-browser/src/dom/events/hammer_gestures.ts

@@ -13,6 +13,12 @@ import {isPresent} from '../../facade/lang';
 
 import {HammerGesturesPluginCommon} from './hammer_common';
 
+/**
+ * A DI token that you can use to provide{@link HammerGestureConfig} to Angular. Use it to configure
+ * Hammer gestures.
+ *
+ * @experimental
+ */
 export const HAMMER_GESTURE_CONFIG: OpaqueToken = new OpaqueToken('HammerGestureConfig');
 
 export interface HammerInstance {
@@ -20,6 +26,9 @@ export interface HammerInstance {
   off(eventName: string, callback: Function): void;
 }
 
+/**
+ * @experimental
+ */
 @Injectable()
 export class HammerGestureConfig {
   events: string[] = [];

modules/@angular/platform-browser/src/dom/events/key_events.ts

@@ -23,6 +23,10 @@ var modifierKeyGetters: {[key: string]: (event: KeyboardEvent) => boolean} = {
   'shift': (event: KeyboardEvent) => event.shiftKey
 };
 
+
+/**
+ * @experimental
+ */
 @Injectable()
 export class KeyEventsPlugin extends EventManagerPlugin {
   constructor() { super(); }