This updates to the latest version of pdfjs-dist.  The previous versions 
had a bug that caused cross site loading issues for some webpack builds.

With the newer version of pdfjs-dist, using the default EventBus has 
been deprectated. This sends in our own eventBus to manage the event 
messages.

The ES6 version requires support of ReadableStream causing issues.  
Rather than using a polyfill or mocking this, we should just assume that 
it has been compiled to a working syntax, which for the tests is ES5.

The updated pdfjs-dist library added an unscore to the location of the 
pageIndex.  This happens in real time, but since we are mocking it in 
the tests, we need to make sure to mock it correctly.

This is done to match the need to manually set the eventBus on a 
LinkService