Density tracking issue: #18078
This PR refactors our spacing system to use a more flexible and
maintainable approach. We've replaced the static `Spacing` enum with a
dynamically generated `DynamicSpacing` enum using a proc macro.
Enum variants now use a `BaseXX` format, where XX = the pixel value @
default rem size and the default UI density.
For example:
`CustomSpacing::Base16` would return 16px at the default UI scale &
density.
I'd love to find another name other than `Base` that is clear (to avoid
base_10, etc confusion), let me know if you have any ideas!
Changes:
- Introduced a new `derive_dynamic_spacing` proc macro to generate the
`DynamicSpacing` enum
- Updated all usages of `Spacing` to use the new `DynamicSpacing`
- Removed the `custom_spacing` function, mapping previous usages to
appropriate `DynamicSpacing` variants
- Improved documentation and type safety for spacing values
New usage example:
```rust
.child(
div()
.flex()
.flex_none()
.m(DynamicSpacing::Base04.px(cx))
.size(DynamicSpacing::Base16.rems(cx))
.children(icon),
)
```
vs old usage example:
```
.child(
div()
.flex()
.flex_none()
.m(Spacing::Small.px(cx))
.size(custom_spacing(px(16.)))
.children(icon),
)
```
Release Notes:
- N/A
