manually add typed and with_type methods

[ranfdev]

Closes #1384

I've also found DropTarget::new which could receive the same treatment, but that's a more complex case, because it can also accept the type G_TYPE_INVALID when the user wants to specify multiple GTypes, so I've just skipped that.

[jf2048]

Maybe it can be split into DropTarget::new, DropTarget::with_type and DropTarget::with_types?

[bilelmoussaoui]

There are other ones as you can tell from the link i shared in the issue

[bilelmoussaoui]

Please add a note to the changelog as well

[bilelmoussaoui]

Maybe it can be split into DropTarget::new, DropTarget::with_type and DropTarget::with_types?

That is what I ended up doing. It is a much better API :-)

Replaced by #1415