Use skip_serializing_none macro to reduce clutter in helix-dap

[thomasaarholt]

New rust developer here, please be gentle.

I decided to take a look at #6265 to see if there was anything I could help with, and noticed that there were about 200 lines of #[serde(skip_serializing_if = "Option::is_none")] that could be removed using the #[skip_serializing_none] macro. It's now a lot easier to parse it, at least to my eyes.

I wasn't sure whether to add cargo.lock or not, so I added it in a separate commit.

[pascalkuthe]

From a functional perspective, this seems fine. However, we usually don't want to add new dependencies if it can be avoided. Both to avoid additional compile time hits and to reduce the need to maintain and audit them. There is of course no hard rule but generally the rule of thumb is: If a dependency just saves us writing a couple lines of trivial code its not worth it.

I think both for DAP we never actually want to send None values so one way to solve this without requiring additional proc macros/dependencies would be to simply write our own serializer to wraps the serde_json serializer and always ignore None values. So that could be way to reduce the noise here and avoid accidently forgetting there annotations.

[thomasaarholt]

I understand, that makes sense. I’m not sure I can commit to that sort of thing right now, but I will take a look.