Image loading and caching

[MartinZikmund]

Discussed in #18190

^{Originally posted by ForkBug September 12, 2024}
In maui, the best practice to display an image is using FFImageLoading, which provides lazy loading, cache, and automatic downsampling.

In Uno, ImageEx and ImageCache from Windows Community Toolkit provide lazy loading and cache. But no automatic downsampling.

What's the best practice in Uno to show an image?

[MartinZikmund]

We need to:

1. Integrate a more general solution to image loading and caching that behaves reliably across targets
2. Add documentation on how external libraries for this purpose can be utilized