Separate Core MAUI platform and Native Controls

[Martinn2]

IMHO, MAUI platform SDKs should be separated from Native Controls.
It would be used like this:
.UseMauiCore()
.UseMauiNativeControls()

This way, MAUI might support Linux (and maybe web) just by adding "Maui Core" for now, so support would be easier and faster.
To create UI, we would then use Blazor,Microsoft.Maui.Graphics.Controls, or any similar library (for example Syncfusion has a lot of drawn controls).

Also developers who would like to use drawn controls on other platforms would make their projects smaller maybe by removing XAML at all.