Model required currency/unit options for Intl.NumberFormat currency/unit styles

[Copilot]

Intl.NumberFormatOptions allowed style: "currency" without a currency string (or with currency: undefined), which compiles cleanly under --strict but throws TypeError: Currency code is required with currency style. at runtime. Same gap exists for style: "unit" / unit.

// Previously compiled fine, threw at runtime:
new Intl.NumberFormat("en", { style: "currency", currency: undefined });

Changes

• Added a new extensible registry, NumberFormatOptionsStyleRequiredOptionsRegistry (lib.es5.d.ts), mapping each style name to the extra properties required for that style (currency: { currency: string } in lib.es5.d.ts, unit: { unit: string } added in lib.es2020.intl.d.ts).
• NumberFormatConstructor's call/construct signatures are now generic over the options object, intersecting it with NumberFormatOptionsStyleRequiredOptions<T["style"]> computed from the registry — mirrors the discriminated-overload pattern already used elsewhere in lib.d.ts (e.g. addEventListener), avoiding a breaking rewrite of NumberFormatOptions into a full union that would conflict with its declaration-merging registry pattern across lib versions.
• supportedLocalesOf is left untouched, since it doesn't perform this runtime validation.
• Non-literal option bags (e.g. a variable typed as NumberFormatOptions) are unaffected — the check only applies when style is inferred as a literal from an object literal argument.

new Intl.NumberFormat("en", { style: "currency", currency: "USD" }); // ok
new Intl.NumberFormat("en", { style: "currency" }); // error: currency required
new Intl.NumberFormat("en", { style: "unit", unit: "kilogram" }); // ok
new Intl.NumberFormat("en", { style: "unit" }); // error: unit required

Tests

• Added intlNumberFormatRequiredStyleOptions.ts covering both new error cases and previously-valid usages that must remain unaffected.

• Fixes Intl.NumberFormat does not model required properties when style is set to currency #57514