Splash screen docs confusing / out of date

The splash screen docs were a bit confusing for me to follow, bu I think mostly because some of the information is out of date.

https://learn.microsoft.com/en-us/dotnet/maui/user-interface/images/splashscreen?view=net-maui-7.0&tabs=android

It was unclear when the IDE was expected to auto-generate some of the properties vs. when they should be manually included and this led to some confusion and wrangling.

For Android, I believe the process has changed in later versions so a general review would be good. For example, the doc references `Resourcs/values/maui_colors.xml` and `Resources/drawable/maui_splash_image.xml`; the former still exists as just `Resourcs/values/colors.xml` but AFAICT the latter does not seem to exist whatsoever.

I also ended up adding a png and referencing it as png in the csproj as well (instead of svg as the docs seemed to suggest)

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* ID: 44323c6e-d65c-b254-ee3c-cd9415bdf3bc
* Version Independent ID: 44323c6e-d65c-b254-ee3c-cd9415bdf3bc
* Content: [Add a splash screen to a .NET MAUI app project - .NET MAUI](https://learn.microsoft.com/en-us/dotnet/maui/user-interface/images/splashscreen?view=net-maui-7.0&tabs=android)
* Content Source: [docs/user-interface/images/splashscreen.md](https://github.com/dotnet/docs-maui/blob/main/docs/user-interface/images/splashscreen.md)
* Product: **dotnet-mobile**
* Technology: **dotnet-maui**
* GitHub Login: @davidbritch
* Microsoft Alias: **dabritch**