dumpCell returns paths with mixed slashes on Windows

[roblourens]

Debugging with Jupyter on Windows (via vscode-jupyter), and I'm having issues because we get paths that have mixed slashes from dumpCell, but if we send a request to set a breakpoint in that path, it is not accepted by debugpy unless we normalize the slashes

Example

[Debug] to kernel: {"command":"dumpCell","arguments":{"code":"print(1)\nprint(2)\nprint(3)\nprint(4)\nprint(5)"},"type":"request","seq":8}
[Debug] response: {"type":"response","request_seq":8,"success":true,"command":"dumpCell","body":{"sourcePath":"C:\\Users\\roblou\\AppData\\Local\\Temp/ipykernel_1952/1680877720.py"}}

We can normalize the paths on the client, we were doing that, but it broke down for example when debugging a windows kernel from a non-windows machine. I can also fix that, but really the client should be able to set a breakpoint with the exact path it received without having to transform it.

I'm happy to attempt a PR if you point me in the right direction.

[roblourens]

Sorry, I picked an environment with an old ipython, and I see this is already fixed in #784