Generated Android Manifest does not include placeholder for android:icon when using QT_ANDROID_APP_ICON

When using QT_ANDROID_APP_ICON (introduced in Qt 6.9), the generated AndroidManifest.xml does not include the android:icon property. This is expected for a new empty project with no icons. However, when icons are later added to the project (e.g., under /android/res/drawable/), Qt Creator automatically inserts:

android:icon="@drawable/icon" 

Instead, the Manifest generator could include a placeholder:

android:icon="-- %%INSERT_APP_ICON%% --" 

and

set_target_properties(apptest_manifest    PROPERTIES    QT_ANDROID_APP_ICON "@drawable/icon") 

Update the Manifest generation logic to always include the android:icon placeholder:

• Ensure that the placeholder is replaced only when QT_ANDROID_APP_ICON is explicitly set.
• update the CMakeLists.txt to include the QT_ANDROID_APP_ICON property when icons are detected.