MatPaginator doesn't emit PageEvent when pageIndex is altered programmatically

[snebjorn]

Bug, feature request, or proposal:

Bug.

What is the expected behavior?

When

@Input()
pageIndex: number

changes

@Output()
page: EventEmitter<PageEvent> // from doc: Event emitted when the paginator changes the page size or page index.

should emit a PageEvent.

What is the current behavior?

No PageEvent is emitted.

What are the steps to reproduce?

Component:

@ViewChild(MatPaginator) paginator: MatPaginator;

ngAfterViewInit(): void {
    this.paginator.page.subscribe(x => console.log(x));
  }

test() {
    this.paginator.pageIndex = 42;
  }

View
<button (click)="test()">TEST</button>

Clicking the button should result in a PageEvent being written to the console. But nothing happens

What is the use-case or motivation for changing an existing behavior?

According to the documentation an event should be emitted when either page size or page index changes.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

     _                      _                 ____ _     ___
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/


Angular CLI: 6.1.2
Node: 9.10.1
OS: win32 x64
Angular: 6.1.0
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.7.1
@angular-devkit/build-angular     0.7.1
@angular-devkit/build-optimizer   0.7.1
@angular-devkit/build-webpack     0.7.1
@angular-devkit/core              0.7.1
@angular-devkit/schematics        0.7.1
@angular/cdk                      6.4.2
@angular/cli                      6.1.2
@angular/flex-layout              6.0.0-beta.17
@angular/material                 6.4.2
@ngtools/webpack                  6.1.1
@schematics/angular               0.7.2
@schematics/update                0.7.2
rxjs                              6.2.2
typescript                        2.9.2
webpack                           4.9.2

[crisbeto]

Will be resolved by #12586.

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