Added support for nested scrolling in a CoordinatorLayout

[Cilenco]

It is disabled by default. You have to call setNestedScrollingEnabled(true) manually!

[AshishPaul]

@barteksc Hi, first of all, Thank you for this awesome library and the hard work you've put into this as well as other contributors.
I just wanted to know if this PR is going to get merged. I need this functionality in my app. Thanks to @Cilenco

[kartikj07]

Thank you soo much, @Cilenco this solution works great.

But when used with CollapsingToolbarLayout, the collapse works properly, but when the top of the PDF is reached the collapsed view doesn't start to reappear. Any ideas for it??

[akaita]

This is in no way a replacement for a proper integration with CoordinatorLayout, but as a quick workaround I did:

pdfView.fromStream(myStream)
.onPageScroll { page, positionOffset ->
                            val topReached = page == 0 && positionOffset == 0f
                            appBarLayout.setExpanded(topReached, true)
                        }
.load()

Kinda does the trick