Add registered symbol cases to method and accessor name tests

[hexbinoct]

Closes #3436.

The method and accessor fn-name tests check .name for methods keyed by a unique symbol (Symbol('test262') gives [test262]) and by an anonymous one (the empty string), but never by a registered symbol from Symbol.for. SetFunctionName treats both kinds the same way: a Symbol key becomes its [[Description]] in brackets, and Symbol.for stores its key string as the description. XS got this wrong for registered symbols and returned the description without brackets (Moddable-OpenSource/moddable#876), which is where this issue came from.

This adds a Symbol.for('registered') key next to the existing unique-symbol key in the eight tests that cover methods and accessors:

• object literal methods and generator methods
• class methods and generator methods, prototype and static
• object literal and class getters and setters, prototype and static

Each gets the same verifyProperty check as its unique-symbol neighbour, expecting [registered] (or get [registered] / set [registered]).

I left the fn-name-arrow, -class, -cover, -fn and -gen tests for property assignments like { [sym]: function () {} } alone, since those reach SetFunctionName through NamedEvaluation, not DefineMethod, and the issue is about methods. Happy to extend them too if that is wanted.

Checked locally with Node and engine262: all eight pass, and each one fails on both when its expected value is changed to the XS output (registered without brackets). Thanks to gibson042 for the report and the XS repro.

LLM disclosure: Claude Opus 5.5 helped me find the gap, write the change and check it; I reviewed the result.

[github-actions]

8 new or modified tests were run on 7 engines.

View workflow run

Test	Engine262	GraalJS	JavaScriptCore	QuickJS	SpiderMonkey	V8	XS
language/expressions/object/fn-name-accessor-get.js	✅	✅	✅	✅	✅	✅	✅
language/expressions/object/fn-name-accessor-set.js	✅	✅	✅	✅	✅	✅	✅
language/expressions/object/method-definition/fn-name-fn.js	✅	✅	✅	✅	✅	✅	✅
language/expressions/object/method-definition/fn-name-gen.js	✅	✅	✅	✅	✅	✅	✅
language/statements/class/definition/fn-name-accessor-get.js	✅	✅	✅	✅	✅	✅	✅
language/statements/class/definition/fn-name-accessor-set.js	✅	✅	✅	✅	✅	✅	✅
language/statements/class/definition/fn-name-gen-method.js	✅	✅	✅	✅	✅	✅	✅
language/statements/class/definition/fn-name-method.js	✅	✅	✅	✅	✅	✅	✅