Fix exotic get_own_property descriptor presence flags

[yorkie]

Set QuickJS JS_PROP_HAS_* bits when returning descriptors from exotic class get_own_property hooks, preventing descriptor consumers such as Object.keys() and Object.getOwnPropertyDescriptor() from reading invalid descriptor state.

Extend the handwritten exotic class test to cover enumerable own property names, Object.keys(), writable data descriptors, and accessor descriptors.

[Copilot]

Pull request overview

This PR fixes QuickJS property descriptor presence handling for exotic classes by ensuring JS_PROP_HAS_* bits are set when returning property descriptors from exotic_get_own_property, so descriptor consumers (e.g. Object.keys(), Object.getOwnPropertyDescriptor()) see valid/consistent descriptor shapes. It also extends the existing exotic-class test to cover enumerable own property names, Object.keys(), writable data descriptors, and accessor descriptors.

Changes:

• Set JS_PROP_HAS_GET/JS_PROP_HAS_SET for get/set descriptors and JS_PROP_HAS_VALUE for data descriptors returned from the exotic get_own_property hook.
• Extend the exotic-class test to include an accessor property and additional descriptor/key enumeration assertions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
core/src/class/ffi.rs	Updates descriptor flag construction for exotic get_own_property results.
core/src/class.rs	Extends exotic-class test coverage for keys and property descriptors (data + accessor).

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