scrolledwindow: add ::max-content-width and -height properties

scrolledwindow: add ::max-content-width and -height properties

The GtkScrolledWindow has support to set the minimum content size (both
width and height) which controls the minimum space allocated, but does
not exposes any way to control the maximum size the content can grow.

After the introduction of GtkPopover, which always uses the minimum
size of it's children widgets, the lack of max-content-width and -height
properties became a concrete use case.

This patch introduces the GtkScrolledWindow::max-content-width and
-height properties. The properties will alter the minimum size of
the scrolled window, making it grow up to the set value. They also
respect the previously set ::min-content-width and -height.

https://bugzilla.gnome.org/show_bug.cgi?id=742281