Implement Web Notification API in src/client

[yorkie]

Feature Request

Implement the Web Notification API in src/client.

Reference:

• Web Notification API Spec: https://developer.mozilla.org/en-US/docs/Web/API/Notification

Requirements:

• Provide a Notification class in C++ (e.g., src/client/dom/notification.hpp/.cpp) with the following features:
  • Constructor: Notification(title, options)
  • Static property: Notification.permission
  • Static method: Notification.requestPermission()
  • Instance properties: title, body, icon, tag, data, requireInteraction, etc.
  • Event handlers: onshow, onclick, onclose, onerror
  • Method: close()
• JS binding so Notification can be constructed from JavaScript.
• Permission model (stub is acceptable for first step).
• On desktop: use native notification APIs (e.g., macOS NSUserNotification, Windows Toast Notification, Linux libnotify). On XR: use JSAR internal popup or 3D UI.
• Support event delivery to JS via callback.
• Follow the API shape and behavior described in the MDN documentation and Chromium's implementation:
  • Chromium Notification API implementation

Implementation Notes:

• See Chromium's Notification class for reference: notification.cc
• JSAR should aim for spec-compliant behavior and extensibility for XR/3D notification display.

Acceptance Criteria:

• JavaScript code can construct new Notification instances with options.
• Notifications display appropriately on all platforms JSAR supports (desktop and XR).
• Permission model is present (even if stub).
• All standard events are supported and delivered to JS.
• API is documented and tested.

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Web spec: https://www.w3.org/TR/notifications/
MDN: https://developer.mozilla.org/en-US/docs/Web/API/Notification
Chromium implementation: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/modules/notifications/notification.cc