Feature addition: text along path

[philocalyst]

Closes #395

This PR adds rigid text and content placement along named/inline paths.

What changed

• Measures line and Bézier paths by arc length.
• Supports grapheme-level text placement with preserved styles.
• Keeps opaque content such as math and boxes intact.
• Supports alignment, tracking, spacing modes, reversal, upright text, overflow handling, and kerning.
• Handles sharp corners with padding, skipping, or direct traversal.
• Reuses draw.content styles and resolved metrics.
• Adds tests for path measurement, Bézier scaling, corners, overflow, wrappers, and rendering.
• Adds gallery and manual documentation entries.

My notes on design

I heavily referenced Typst's existing approach of separating measurement form layout, reusing resolved content styles. The arc-length sampler uses adapative subdivision + Newton refinement, which mirrors the spirit of the work done in
Design notes within Typst PR #3847 (typst/typst#3847).

The layout code maintains opaque content rigid, avoiding pretending that independently shaped grapheme clusters can effectively preserve cross-place ligatures.

Now, on the note about FIXED, as of right now Typst doesn't have a general way of doing deeper text pathing manipulation. I looked into doing some WASM black magic, but hey, that's not really what the project is about! So instead I just got a PR up at Typst, which if/when merged will make that part very easy to add.

[johannes-wolf]

Thank you, this is a great addition! I will review the PR soon :).

[philocalyst]

Thank you! Going to go in and fix the CI in the meantime :)

Aside: was hapily surprised how mostly readable the typst code is, this being the first time I tried to write something serious in it, but let me know if any sections are too hard to parse!

[philocalyst]

Okay hm it seems to fail on master too, so you know!