Remove "returns null when content disposition is form-data".
The name of the test is already misleading: It suggests that
the return value is null if the Content-Disposition starts with
"form-data". This is not the case, anything with the "filename"
parameter is accepted.
So, to correct this, one would have to rephrase the test description to
"returns null when content disposition has no filename".
But this is already tested by the test called
"gets the filename from the response header".
So, remove the test.
This patch updates the `IPDFStreamReader` interface and ensures that the interface/implementation of `network.js`, `fetch_stream.js`, `node_stream.js`, and `transport_stream.js` all match properly.
The unit-tests are also adjusted, to more closely replicate the actual behaviour of the various actual `IPDFStreamReader` implementations.
Finally, this patch adjusts the use of the Content-Disposition filename when setting the title in the viewer, and adds `PDFDocumentProperties` support as well.
