Draft: Modernize EvAnnotationsWindow

This has API change, so has to go in evince-next and depends on !585 (merged)

In addition, there is some UI change, that is still not perfect (it cannot be seen in the screenshots, but the new version the button still does not respect the color on hover. Also, the transparency on the header bar is not amazing when unfocused. Marked as Draft until I fix these things, but feedback gladly welcomed 😄

In addition, this allows changing the size of the annotation window from all the sides, and not just the bottom corners.

Before:

After:

Helps !373