Disallow timeZone option in Temporal.ZonedDateTime.prototype.toLocaleString - #65434

ZonedDateTime#toLocaleString always formats in the receiver's own time zone. JavaScriptCore, SpiderMonkey and V8 all throw TypeError if a timeZone option is passed. The lib typed options as plain Intl.DateTimeFormatOptions, so the bad call type-checked:

const zdt = Temporal.Now.zonedDateTimeISO("America/Chicago");
zdt.toLocaleString(undefined, { timeZone: "Europe/Berlin" });
//                              ~~~~~~~~ now TS2353

Changes

• lib.esnext.temporal.d.ts
  • New Temporal.ZonedDateTimeToLocaleStringOptions extends Omit<Intl.DateTimeFormatOptions, "timeZone"> {}, the shape the issue proposed. It follows the YearMonthLikeObject extends Omit<…> pattern already in this file.
  • ZonedDateTime.toLocaleString now takes this type. The other Temporal types still accept timeZone, matching the spec.
• Tests
  • New temporalZonedDateTimeToLocaleStringTimeZone.ts covers:
    • object literals with timeZone, which now error;
    • valid ZonedDateTime options;
    • an Intl.DateTimeFormatOptions variable, which is still accepted;
    • Instant / PlainDateTime still accepting timeZone.
  • In the existing temporal.ts, the line already marked /* WRONG */ now reports the error.
  • temporal.types reflects the new parameter type.

Design notes

• Why Omit and not timeZone?: never: Omit only rejects timeZone in object literals, through the excess-property check. Values already typed as Intl.DateTimeFormatOptions are still accepted. timeZone?: never (suggested on Reject timeZone in ZonedDateTime.toLocaleString options #64346) would also catch non-literal values, but it would reject every Intl.DateTimeFormatOptions-typed variable. That would break the common const opts: Intl.DateTimeFormatOptions = …; zdt.toLocaleString(l, opts) pattern.
• Error wording: the message names the type Omit<DateTimeFormatOptions, "timeZone"> rather than the interface name. TS 6.0.3 prints the same name for an interface that extends Omit<…>.

• Fixes The options arg of Temporal.ZonedDateTime.prototype.toLocaleString() currently accepts "illegal" option timeZone #64227