feat(globalThis): expose built-in constructors as properties

[proggeramlug]

Summary

• Populate the globalThis singleton with built-in constructor properties on first init so globalThis.Array / context.Object (lodash's runInContext pattern) no longer return undefined.
• Route Expr::PropertyGet { GlobalGet(_), <Builtin> } through js_get_global_this + js_object_get_field_by_name_f64 so the static AST shape sees the same populated singleton (mirrors the IndexGet arm added in perry-runtime: Effect framework SIGSEGVs during Utils.ts module init — array-fast-path called with x0 = 0x1 (Effect end-to-end blocker, post-#592) #611).
• Constructors get a ClosureHeader-backed sentinel (typeof === "function" via the existing CLOSURE_MAGIC tag); Math / JSON / Reflect get a plain ObjectHeader (typeof === "object"). Each constructor carries a prototype dynamic property pointing at an empty backing object so <Builtin>.prototype reads don't trip the spec-shaped TypeError: Cannot read properties of undefined.

Follows PR #963 (v0.5.977) which closed the Function('return this')() IIFE recogniser. Today's blocker for import _ from "lodash" was the next line down — var Array = context.Array; var arrayProto = Array.prototype — because the built-in constructors were never registered as properties on the singleton.

Test plan

• test-files/test_globalthis_builtins.ts — byte-for-byte parity with node --experimental-strip-types for typeof globalThis.{Array,Object,Function,Math,JSON} + Array.prototype + new Array(3).length.
• lodash repro: _.chunk([1,2,3,4], 2) still fails to load _, but the throw point advanced from lodash.js:1463 (var arrayProto = Array.prototype) to lodash.js:1493 (funcToString.call(Object)). The new blocker needs real Function.prototype.toString support — tracked alongside the broader lodash compile-as-package work.

Caveats

• The backing objects are sentinels, not the real constructors. Array.prototype.toString === undefined (Node returns a function).
• globalThis.Array === Array is false. Bare Array still lowers to Expr::GlobalGet(0); the singleton form returns a closure pointer. Unifying these requires widening Perry's first-class representation of built-in constructors.
• Bare new Array(n) is unaffected — it flows through lower_new like before. The thunk underneath each sentinel is a no-op returning undefined, so globalThis.Array(3) as a call (not a new) returns undefined rather than constructing an array (best-effort, known gap).

Version

• Cargo.toml [workspace.package].version → 0.5.978
• CLAUDE.md **Current Version:** → 0.5.978
• CHANGELOG.md — prepended ## v0.5.978 — feat(globalThis): ... block with full context