Add layout expressions for view positions

[ibgreen-openai]

It would be very powerful to be able to use CSS style calc expressions when declaratively specifying view layouts.

Summary

• replace the simple position struct with a LayoutExpression tree plus parser and evaluator so strings with numbers, percentages, px units, and calc() expressions can be represented and evaluated
• store the parsed layout expressions on View and evaluate them when resolving viewport dimensions and padding
• add tape tests that cover literal numbers, percentages, pixels, and calc() combinations as well as direct evaluation of synthetic expression trees

Testing

• NODE_ENV=test node node_modules/@vis.gl/dev-tools/dist/test.js node

---

https://chatgpt.com/codex/tasks/task_i_68fb7cdcc1e8832ca8367f01290541fc

[chrisgervang]

This looks useful. Backwards compatible, aligns with an existing expression syntax, and would work well in any environment.

I could also see this being useful in viewState's padding property (and any screen space prop)

My testing run book for this would be:

• try typing an expression in the JSON playground, noodles.gl (or any reactive environment) to see how graceful it is with syntax errors, and how responsive it feels.
• try it on each view type and each property (the examples you've modified cover this well)