Add a new custom icon

Adding a new custom icon is a lengthy and annoying process.

1. Resize icon to 1024x1024 PNG
2. Run through https://tinypng.com
3. Determine a good name for it: a-z characters only
4. Add to public/alternateIcons and ios/App/App/public/AlternateIcons
5. In Android project, go to Resource Manager -> (plus) -> Image Asset
6. Add image with name to foreground layer source asset

Foreground Layer -> Scaling -> Resize 67%, Trim -> No

Background Layer -> Source Asset = "Image", for image choose 1x1 transparent PNG

7. Add another activity-alias to AndroidManifest.xml
8. For iOS, add image to image assets. IMPORTANT: Append _v2 to name!
9. In appIconSlice.tsx, add icon name to APP_ICONS. Fix resulting typescript errors.