feat: [SDK-5161] expose notification metadata and improve demo coverage

[fadi-george]

Description

One Line Summary

Expose complete action-button and raw notification payload data, and make the demos exercise OneSignal-managed Android grouping.

Details

Motivation

The native iOS SDK returns action-button icons as templateIcon or systemIcon, but the .NET conversion only read icon. The .NET notification model also omitted the native rawPayload exposed by Android and iOS.

For SDK-5128, Android 16 can automatically group otherwise ungrouped notifications. Tapping that system-generated summary may launch the app without OneSignal click data, so the demos need a deterministic OneSignal-managed group.

Scope

• Add nullable TemplateIcon and SystemIcon properties to ActionButton while preserving Android Icon behavior.
• Map iOS template and system icons through one shared action-button converter used by click and foreground-display events.
• Add Notification.RawPayload as parsed key/value data on Android and iOS, including notifications nested under GroupedNotifications.
• Preserve the existing public notification constructors and add raw-payload-aware overloads.
• Bundle template-bookmark-icon.png and template-share-icon.png in the demo app and Notification Service Extension.
• Add android_group: "demo-group" to every maintained demo that sends remote notifications: the main demo, no-location demo, and local-notification plugin demo.
• Align demo notification and IAM event logging with the Capacitor demo, including full event output and foreground prevent/display examples.

Testing

Unit testing

No unit tests were added because the repository currently has no unit-test project or test runner. Native conversion requires platform notification objects, and grouping summary behavior requires device testing.

Build verification

• OneSignalSDK.DotNet.Android builds with zero warnings and errors.
• OneSignalSDK.DotNet.iOS builds with zero warnings and errors.
• Main demo builds for Android and iOS.
• No-location and local-notification plugin demos build for Android.
• CSharpier formatting passes.

Manual testing

Action-button icons

Sent notifications with blank, template, and system action-button icons and verified:

• Android: Icon contains the configured resource name when provided and is null when blank.
• iOS template icon: TemplateIcon is populated; Icon and SystemIcon are null.
• iOS system icon: SystemIcon is populated; Icon and TemplateIcon are null.
• iOS blank icon: all icon properties are null.

Android grouping and raw payload

Sent multiple demo notifications using demo-group, tapped the group summary, and verified:

• The notification click listener fires.
• GroupKey is demo-group.
• GroupedNotifications contains the grouped notifications.
• RawPayload is populated on the summary notification and each grouped notification.

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR changes are related to notification payload parity and demo validation
• Public API changes are explained above and preserve existing constructor signatures

Testing

• I have included test coverage for these changes, or explained why it was not added
• All applicable builds and formatting checks pass
• I have personally tested the platform-specific notification behavior on device

Final pass

• Code is as readable as possible
• I have reviewed this PR myself

[abdulraqeeb33]

Approve with nits. Click and display converters now read templateIcon/systemIcon, and Android still uses the 3-arg ctor so Icon is preserved.

1. The dict-to-ActionButton lookup is pure after NSObjectToPureDict. A shared helper plus fixtures would lock the original key bug.
2. Demo still has no action-button send type, and the handlers do not print ActionButtons. The PNG names (dashboard value without .png) are also unnamed in the README. Fine as a follow-up.