XS: value and done on iterator result objects are non-writable and non-configurable

[d01c2]

Build environment: macOS 26.5.2

Moddable SDK version:

• Installed via jsvu, so there is no SDK source tree / git describe.
• Engine reports: XS 17.9.1, slot 32 bytes, ID 4 bytes

Target device: desktop (host xs)

Description
The value and done properties of an iterator result object are created as non-writable and non-configurable.

CreateIteratorResultObject adds both with CreateDataPropertyOrThrow, which builds the descriptor { [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: true }, so both properties must be writable and configurable.

Steps to Reproduce

$ xst -e 'print(JSON.stringify(Object.getOwnPropertyDescriptor((function*(){})().next(), "value")))'
{"writable":false,"enumerable":true,"configurable":false}

Expected behavior

{"writable":true,"enumerable":true,"configurable":true}

For comparison, V8 (15.4.18):

$ v8 -e 'print(JSON.stringify(Object.getOwnPropertyDescriptor((function*(){})().next(), "value")))'
{"writable":true,"enumerable":true,"configurable":true}

Other information
done has the same descriptor, and every iterator result object is affected, not only generators. The results of the array, string, Map, Set, RegExp string and iterator helper next methods all report writable: false, configurable: false. The difference reaches ordinary code, since writing to the result throws in strict mode:

$ xst -e '"use strict"; var r = [1].values().next(); r.value = 9;'
TypeError: set value: not writable