Model Intl.Collator#compare as a readonly bound function property

[Copilot]

Intl.Collator#compare was declared as a method, but per ECMA-402 it is a getter returning a function bound to the collator, with no setter. The method form makes detached usage look receiver-dependent (the cause of typescript-eslint's unbound-method false positive) and permits assignment the platform doesn't allow.

Changes

• lib.es5.d.ts: compare is now a readonly function-valued property with this: void:

  interface Collator {
      readonly compare: (this: void, x: string, y: string) => number;
      resolvedOptions(): ResolvedCollatorOptions;
  }

• New compiler test intlCollatorCompare.ts covering call-through, detached call, Array.prototype.sort passthrough, and assignment (now TS2540).

const { compare } = new Intl.Collator("en");
["b", "a"].sort(compare);        // ok, and no longer looks unbound
collator.compare = (x, y) => 0;  // error TS2540: read-only property

No other baselines changed.

• Fixes Intl.Collator#compare method type does not match spec #62048