[dotnet] use **FromWorkload** for targeting/runtime pack versions

Context: dotnet/sdk#19596
Context: dotnet/android#6184

If we use the version number string of `**FromWorkload**`, then our
runtime packages don't need to be resolved from a NuGet feed. They can
be resolved from the `dotnet/packs` directory.

This completely eliminates the need for a `NuGet.config` file when
building a .NET 6 app with a local build of the xamarin-macios.

You will no longer need a feed such as:

    <add key="local-dotnet-feed" value="~/src/xamarin-macios/_build/nuget-feed" />

Author: jonathanpeppers

dotnet/targets/Xamarin.Shared.Sdk.DefaultItems.targets

@@ -85,10 +85,10 @@
     <KnownFrameworkReference Include="Microsoft.$(_PlatformName)"
                             TargetFramework="net6.0"
                             RuntimeFrameworkName="Microsoft.$(_PlatformName)"
-                            DefaultRuntimeFrameworkVersion="$(_ShortPackageVersion)"
-                            LatestRuntimeFrameworkVersion="$(_ShortPackageVersion)"
+                            DefaultRuntimeFrameworkVersion="**FromWorkload**"
+                            LatestRuntimeFrameworkVersion="**FromWorkload**"
                             TargetingPackName="Microsoft.$(_PlatformName).Ref"
-                            TargetingPackVersion="$(_ShortPackageVersion)"
+                            TargetingPackVersion="**FromWorkload**"
                             RuntimePackNamePatterns="Microsoft.$(_PlatformName).Runtime.**RID**"
                             RuntimePackRuntimeIdentifiers="$(_RuntimePackRuntimeIdentifiers)"
                             Profile="$(_PlatformName)"

tests/dotnet/Makefile

@@ -6,7 +6,6 @@ include $(TOP)/Make.config
 # and to put any extracted packages in the 'packages' directory (to not clutter up ~/.nuget/packages)
 NuGet.config: $(TOP)/NuGet.config Makefile
 	$(Q) $(CP) $< $@.tmp
-	$(Q) nuget sources add -Name local-dotnet-feed -Source $(abspath $(DOTNET_FEED_DIR)) -ConfigFile $@.tmp
 ifdef CUSTOM_DOTNET
 	$(Q) nuget sources add -Name dev-runtime-feed -Source $(abspath $(DOTNET_RUNTIME_PATH)/artifacts/packages/Release/Shipping) -ConfigFile [email protected]
 endif