[dotnet] Make 'Full' the default link mode for NativeAOT. (#18734)

Make 'Full' the default link mode for all platforms for NativeAOT because:

* It will achieve the best app size.
* NativeAOT is not a drop-in replacement that's guaranteed to work - there are
  already known features NativeAOT don't support (and may never support), so
  this may be an opportunity for app developers (and component vendors) to
  make their products trimmer safe.
* NativeAOT will be in preview in .NET 8, so we can change our mind later if
  it turns out to cause too many problems.
* In some cases NativeAOT might require trimming, because we may
  optimize/rewrite assemblies to be NativeAOT-compatible to support existing
  libraries.

This requires #18666 to be merged first, so that ests aren't linked away.

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -1641,8 +1641,7 @@
 		</PropertyGroup>
 		<PropertyGroup Condition="'$(TrimMode)' == ''">
 			<!-- Linking is always on for all assemblies when using NativeAOT - this is because we need to modify all assemblies in the linker for them to be compatible with NativeAOT -->
-			<_DefaultLinkMode Condition="'$(_UseNativeAot)' == 'true' And '$(_PlatformName)' == 'macOS'">Full</_DefaultLinkMode>
-			<_DefaultLinkMode Condition="'$(_UseNativeAot)' == 'true' And '$(_PlatformName)' != 'macOS'">SdkOnly</_DefaultLinkMode>
+			<_DefaultLinkMode Condition="'$(_UseNativeAot)' == 'true'">Full</_DefaultLinkMode>
 
 			<_DefaultLinkMode Condition="'$(_UseNativeAot)' != 'true' And '$(_PlatformName)' == 'macOS'">None</_DefaultLinkMode> <!-- Linking is off by default for macOS apps -->
 			<_DefaultLinkMode Condition="'$(_UseNativeAot)' != 'true' And '$(_PlatformName)' == 'MacCatalyst' And '$(Configuration)' == 'Release'">SdkOnly</_DefaultLinkMode> <!-- Default linking is on for release builds for Mac Catalyst apps -->