Document a few new SDK properties customers affecting Maui and xplat compilation

[marcpopMSFT]

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DisableTransitiveFrameworkReferenceDownloads
Microsoft.Maui.Essentials
EnableWindowsTargeting
NETSDK1100

Describe the new article

@tdykstra, this PR makes three changes we want documentation on: dotnet/sdk#25358

1. If a customer wants to build a windows application (WPF, Winforms) on a non-windows platform, they will get NETSDK1100 today. We've changed the behavior so that if they set <EnableWindowsTargeting>true</EnableWindowsTargeting>, this will enable them to get unblocked. This is because we don't automatically download targeting and runtime packs on platforms that aren't supported but with this flag, we now will when cross-targeting.
2. If a customer has a reference to a project that uses Maui essentials but haven't set <UseMauiEssentials>true</UseMauiEssentials>, then they will need to. We can't flow the maui essentially dependencies automatically without breaking other scenarios but setting this will make sure that the referencing project correctly pulls in the right known framework reference for maui essentialls.
3. We added DisableTransitiveFrameworkReferenceDownloads. Setting this to true will let customers avoid downloading extra runtime and targeting packs they didn't need. For some Maui windows scenarios, it was trying to download aspnet and windows desktop packages just in case they were needed later and this will disable that unless directly used.

[marcpopMSFT]

CC @dsplaisted to review this when the documentation is ready.