Try searching for "docking layout" with a dash of "Visual Studio" (the drop target hints presented by the original, non-Code version are quite good at letting the user figure out exactly where the dragged window will attach).

One example is https://github.com/node-projects/dock-spawn-ts , but there are many more. Maybe you can also tease out the layout logic from VS Code or Theia (or even better, someone else might have done the work).