Replace optional values with defaults when unset

[Eskaan]

As noted in the todo, you should now be able to leave out most of the config.

I will set this as ready in a few seconds, just need to test it (and with it the whole pr).

[Eskaan]

Current default config (click to expand)

// Full verbose version
(
  name: "Default",
  flip: None,
  rotate: North,
  reserve: None,
  columns: Columns(
    flip: None,
    rotate: North,
    main: Some(Main(
      count: 1,
      size: Ratio(0.5),
      flip: None,
      rotate: North,
      split: Some(Vertical),
    )),
    stack: Stack(
      flip: None,
      rotate: North,
      split: Some(Horizontal),
    ),
    second_stack: None,
  ),
)

// Full version (no `Some`)
(
  name: "Default",
  flip: None,
  rotate: North,
  reserve: None,
  columns: Columns(
    flip: None,
    rotate: North,
    main: Main(
      count: 1,
      size: Ratio(0.5),
      flip: None,
      rotate: North,
      split: Vertical,
    ),
    stack: Stack(
      flip: None,
      rotate: North,
      split: Horizontal,
    ),
    second_stack: None,
  ),
)

Here a screenshot:
(Only window order is relevant)

The #[serde(default) macro uses the Struct's Default implementation and uses them to add missing struct fields. This is also the reason why not all Options default to None but to the default for the field from the parent struct. I think this is a good solution.

This way, can also leave placeholders by specifying () for structs.
Here a config example with explanation:

layouts: [
  "Foo",
  "Default"
],
layout_definitions: [
  (
    name: "Foo",
    reserve: ReserveAndCenter,
    columns: (
        main: Main(size: 0.4, split: Horizontal),
        stack: (), // No values set => `Stack`s default impl is used on all fields
        second_stack: (split: Horizontal),
        // `rotate` is unset, columns' default impl for the `rotate` field is used
    )
  ),
  (), // No values set => default config (with name "Default")
],

[hertg]

Thanks for testing it out! :)