test: add tests dbus notification images (#43938)

Provide a NativeImage icon in the notification tests and then inspect
the DBus message payload's `image_data` hint to see if it's correct.
This adds test coverage for LibnotifyNotification::Show() and for
GdkPixbufFromSkBitmap().

spec/api-notification-dbus-spec.ts

@@ -9,8 +9,12 @@
 import { expect } from 'chai';
 import * as dbus from 'dbus-native';
 import { app } from 'electron/main';
+import { nativeImage } from 'electron/common';
 import { ifdescribe } from './lib/spec-helpers';
 import { promisify } from 'node:util';
+import * as path from 'node:path';
+
+const fixturesPath = path.join(__dirname, 'fixtures');
 
 const skip = process.platform !== 'linux' ||
              process.arch === 'ia32' ||
@@ -92,6 +96,7 @@ ifdescribe(!skip)('Notification module (dbus)', () => {
         title: 'title',
         subtitle: 'subtitle',
         body: 'body',
+        icon: nativeImage.createFromPath(path.join(fixturesPath, 'assets', 'notification_icon.png')),
         replyPlaceholder: 'replyPlaceholder',
         sound: 'sound',
         closeButtonText: 'closeButtonText'
@@ -117,6 +122,7 @@ ifdescribe(!skip)('Notification module (dbus)', () => {
         actions: [],
         hints: {
           append: 'true',
+          image_data: [3, 3, 12, true, 8, 4, Buffer.from([255, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 0, 76, 255, 0, 255, 0, 0, 0, 255, 0, 0, 0, 0, 0, 38, 255, 255, 0, 0, 0, 255, 0, 0, 0, 0])],
           'desktop-entry': appName,
           urgency: 1
         }