Add minimum sketch block AST and parsing

[jtran]

Part of #8185.

Adds a new AST node type called SketchBlock and parsing it the same as a function call, followed by a curly brace delimited block. This intentionally reuses existing code. This PR doesn't add any other new sketch block parsing features like var or ==.

@settings(experimentalFeatures = allow)

sketch(XY, keywordArgs = "they parse") {
  // Code here
}

Both parse and execution warnings are generated. You can use @settings(experimentalFeatures = allow) to turn them off.

Execution isn't done. Even evaluating arguments isn't done.

I've used the string TODO: sketch-api: to indicate things that we should come back to.

This should make #4015 easier.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Preview	Comments	Updated (UTC)
modeling-app	Ready	Preview	Comment	Aug 30, 2025 1:27am

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #8171 will not alter performance

_{Comparing jtran/sketch-ast (d73d0d0) with main (bcb6ed2)}

Summary

✅ 89 untouched benchmarks

[jtran]

The code in this function didn't change semantically. I just factored it out to a function.