Reland "Add launch screen to iOS apps"

This is a reland of bf8dad281e724324d774aa4753a674a5a597b0b8

Original change's description:
> Add launch screen to iOS apps
> 
> Bug: skia:
> Change-Id: I7ebe94213c26c31c1b0dbd1b8951f87263cd41a3
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/175826
> Commit-Queue: Jim Van Verth <jvanverth@google.com>
> Reviewed-by: Hal Canary <halcanary@google.com>

Bug: skia:
Change-Id: I111242899339186fba2b8753ee43bc0fb2ea5295
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/239437
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
6 files changed