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/facade/src/lang.ts

@@ -59,6 +59,9 @@ var _global: BrowserNodeGlobal = globalScope;
 
 export {_global as global};
 
+/**
+ * @stable
+ */
 export var Type = Function;
 
 /**
@@ -66,6 +69,8 @@ export var Type = Function;
  *
  * An example of a `Type` is `MyCustomComponent` class, which in JavaScript is be represented by
  * the `MyCustomComponent` constructor function.
+ *
+ * @stable
  */
 export interface Type extends Function {}