Tracking: Layout and Text

## Layout and Text

This issue tracks improvements the Blitz's layout engine (including text/inline layout).

### Block-level layout (Taffy)

Improvements which will happen primarily in [Taffy](https://github.com/DioxusLabs/taffy). See also: the [Taffy roadmap issue](https://github.com/DioxusLabs/taffy/issues/345) in the Taffy repo.

- [x] [`calc` values](https://github.com/DioxusLabs/taffy/issues/225)
- [x] z-index (non-direct siblings)
- [x] [Direction](https://github.com/DioxusLabs/taffy/issues/213)
- [x] "safe" alignment keywords
- [x] https://github.com/DioxusLabs/taffy/issues/709
- [ ] Intrinsic sizing keywords (min-content, max-content, fit-content())
- [ ] [`position: static`](https://github.com/DioxusLabs/taffy/issues/212)
- [ ] `position: fixed`
- [ ] [writing-mode](https://github.com/DioxusLabs/taffy/issues/752)
- [ ] CSS Subgrid layout

### Text/inline layout (Parley)

Improvements which will happen primarily in [Parley](https://github.com/linebender/parley). See also: the [Blitz tracking issue](https://github.com/linebender/parley/issues/208) in the Parley repo.

- [x] `text-wrap-mode`
- [ ] `vertical-align`
- [ ] Subscript and superscript
- [ ] Margin/border/padding for inline spans (should be bidi-aware)

### Cross-cutting (Taffy AND Parley)

Improvements which need to happen in both [Taffy](https://github.com/DioxusLabs/taffy) and [Parley](https://github.com/linebender/parley)

- [x] Floats (https://github.com/DioxusLabs/taffy/issues/437 and https://github.com/linebender/parley/issues/99)
- [ ] Improved baseline alignment

### Other

Improvements which will happen directly in Blitz

- [x] Table improvements
- [x] `table-layout: fixed`
- [x] Support for `border-collapse: collapse`

Start by reading the relevant Taffy roadmap issue or the Parley tracking issue, depending on which unchecked layout item you choose. Confirm the selected improvement's scope with the linked project before starting; done means the corresponding checklist item can be marked complete after the change lands in Taffy, Parley, or Blitz.

Written by the indexing model from the issue text.