Normative: Remove support for nested time zone property bags

Previously, "nested" time zone property bags were unwrapped up to one
level. That is, this object:
{
  timeZone: {
     // ...Temporal.TimeZone methods
  }
}
would not be considered to implement the TimeZone protocol, but would have
its timeZone property used instead, if it were passed to an API that
required a TimeZone protocol object.

These nested property bags are no longer supported. Discussion:
tc39#2104 (comment)

See: tc39#2104

docs/timezone.md

@@ -29,7 +29,6 @@ The object must have at least `getOffsetNanosecondsFor()` and `getPossibleInstan
 Any object with those three methods will return the correct output from any Temporal property or method.
 However, most other code will assume that custom time zones act like built-in `Temporal.TimeZone` objects.
 To interoperate with libraries or other code that you didn't write, then you should implement all the other `Temporal.TimeZone` members as well: `toString()`, `toJSON()`, `getOffsetStringFor()`, `getPlainDateTimeFor()`, `getInstantFor()`, `getNextTransition()`, `getPreviousTransition()`, and `toJSON()`.
-Your object must not have a `timeZone` property, so that it can be distinguished in `Temporal.TimeZone.from()` from other Temporal objects that have a time zone.
 
 The identifier of a custom time zone must consist of one or more components separated by slashes (`/`), as described in the [tzdata documentation](https://htmlpreview.github.io/?https://github.com/eggert/tz/blob/master/theory.html#naming).
 Each component must consist of between one and 14 characters.

polyfill/index.d.ts

@@ -1091,7 +1091,6 @@ export namespace Temporal {
    */
   export interface TimeZoneProtocol {
     id: string;
-    timeZone?: never;
     getOffsetNanosecondsFor(instant: Temporal.Instant | string): number;
     getOffsetStringFor?(instant: Temporal.Instant | string): string;
     getPlainDateTimeFor?(instant: Temporal.Instant | string, calendar?: CalendarLike): Temporal.PlainDateTime;
@@ -1106,7 +1105,7 @@ export namespace Temporal {
     toJSON?(): string;
   }
 
-  export type TimeZoneLike = TimeZoneProtocol | string | { timeZone: TimeZoneProtocol | string };
+  export type TimeZoneLike = TimeZoneProtocol | string;
 
   /**
    * A `Temporal.TimeZone` is a representation of a time zone: either an
@@ -1121,7 +1120,7 @@ export namespace Temporal {
    *
    * See https://tc39.es/proposal-temporal/docs/timezone.html for more details.
    */
-  export class TimeZone implements Omit<Required<TimeZoneProtocol>, 'timeZone'> {
+  export class TimeZone implements TimeZoneProtocol {
     static from(timeZone: TimeZoneLike): Temporal.TimeZone | TimeZoneProtocol;
     constructor(timeZoneIdentifier: string);
     readonly id: string;

polyfill/lib/ecmascript.mjs

@@ -1969,19 +1969,11 @@ export const ES = ObjectAssign({}, ES2022, {
 
   ToTemporalTimeZoneSlotValue: (temporalTimeZoneLike) => {
     if (ES.Type(temporalTimeZoneLike) === 'Object') {
-      if (ES.IsTemporalTimeZone(temporalTimeZoneLike)) return temporalTimeZoneLike;
       if (ES.IsTemporalZonedDateTime(temporalTimeZoneLike)) return GetSlot(temporalTimeZoneLike, TIME_ZONE);
       if (ES.IsTemporalCalendar(temporalTimeZoneLike)) {
         throw new RangeError('Expected a time zone object but received a Temporal.Calendar');
       }
-      if (!('timeZone' in temporalTimeZoneLike)) return temporalTimeZoneLike;
-      temporalTimeZoneLike = temporalTimeZoneLike.timeZone;
-      if (ES.Type(temporalTimeZoneLike) === 'Object') {
-        if (ES.IsTemporalCalendar(temporalTimeZoneLike)) {
-          throw new RangeError('Expected a time zone object as the timeZone property but received a Temporal.Calendar');
-        }
-        if (!('timeZone' in temporalTimeZoneLike)) return temporalTimeZoneLike;
-      }
+      return temporalTimeZoneLike;
     }
     const identifier = ES.ToString(temporalTimeZoneLike);
     return ES.ParseTemporalTimeZone(identifier);

spec/timezone.html

@@ -558,16 +558,10 @@ <h1>
       </dl>
       <emu-alg>
         1. If Type(_temporalTimeZoneLike_) is Object, then
-          1. If _temporalTimeZoneLike_ has an [[InitializedTemporalTimeZone]] internal slot, then
-            1. Return _temporalTimeZoneLike_.
           1. If _temporalTimeZoneLike_ has an [[InitializedTemporalZonedDateTime]] internal slot, then
             1. Return _temporalTimeZoneLike_.[[TimeZone]].
           1. If _temporalTimeZoneLike_ has an [[InitializedTemporalCalendar]] internal slot, throw a *RangeError* exception.
-          1. If ? HasProperty(_temporalTimeZoneLike_, *"timeZone"*) is *false*, return _temporalTimeZoneLike_.
-          1. Set _temporalTimeZoneLike_ to ? Get(_temporalTimeZoneLike_, *"timeZone"*).
-          1. If Type(_temporalTimeZoneLike_) is Object, then
-            1. If _temporalTimeZoneLike_ has an [[InitializedTemporalCalendar]] internal slot, throw a *RangeError* exception.
-            1. If ? HasProperty(_temporalTimeZoneLike_, *"timeZone"*) is *false*, return _temporalTimeZoneLike_.
+          1. Return _temporalTimeZoneLike_.
         1. Let _identifier_ be ? ToString(_temporalTimeZoneLike_).
         1. Let _parseResult_ be ? ParseTemporalTimeZoneString(_identifier_).
         1. If _parseResult_.[[Name]] is not *undefined*, then