Handle AppIcon per platform

[pictos]

Right now for 4.9, we make sure that ForegroundScale will have a variation per platform but still uses the Skia code to re-scale the asset. We've an opportunity to make this even more platform-specific, handling that using whatever the platform exposes to us.

On Android, for example, we can do that inside the splash drawable xml file, using the android:inset attribute, so we can create this xml when user specifies the AnroidForegroundScale:

<?xml version="1.0" encoding="utf-8"?>
<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
  <background android:drawable="@color/ic_launcher_background"/>
  <foreground>
    <inset
      android:drawable="@drawable/ic_launcher_foreground"
      android:inset="16%" />
  </foreground>
</adaptive-icon>

And we can extend that for platforms that exposes ways to customize the app icon