I am using the Gnome desktop environment and I see that it is lacking a lot of features that I think are not so hard to implement. One of these features is the ability to drag and drop files to applications opened in the dock. I simply want when I drag a file over an open app in the dock that the app gets displayed on the screen so that I can drop the file inside it. It is a very important feature for me and I think that it can be done with just a few lines of code. Also, another feature is the ability to see the opened windows of an app just by hovering with the mouse cursor on the app icon in the dock. So, is there any third party software or packages that do these functions? And if not, is there any guide on how to edit the Gnome source code to do so?
Well, Gnome itself doesn't provide any default dock. You are probably talking about some extension developed by the community, e.g. Dash to Dock or something similar. In that case, determine what extension are you using and create a new issue in the relevant issue tracker. It is always better to contact the developers first and only if they do not respond, create a question on the forums.