Issue 408 - Needs further edits

[ColinT]

This PR addresses #408

The current method of listening to the pagerendered event using @HostListener no longer works. This is because PDFSinglePageViewer now loads one page ahead of the current page. Since the event.source.div is not yet in the DOM, the @HostListener fails.

// utils/event-bus-utils.ts:20
// ...
evt.source.div.dispatchEvent(event); // <-- this fires properly but the HostListener does not receive the dispatched event
// ...

One solution to this is to listen to the eventBus from createEventBus directly in both setupMultipageViewer() and setupSinglePageViewer():

// pdf-viewer.component.ts
const eventBus = createEventBus(PDFJSViewer);

eventBus.on('pagerendered', (e) => {
    this.pageRendered.emit(e);
});

This approach is very different from the current setup, and I am not sure what side effects it may cause. But it is the way recommended by the pdf.js devs: #10230.

[sChupin]

You left some commented code in the PR.
Also, you did not apply similar changes to the 'textlayerrendered' event.
I will create another PR to fix that when I find the time to do it.