Mark referenced packages in SDK as implicitly defined

[hexog]

Add IsImplicitlyDefined="true" to PackageReference tags in Sdk.targets.

Will fix two problems i had with C# scripting.

1. Prevent Package Manager in Visual Studio from trying to update SDK packages

When viewing installed packages in IDE, Package Manager suggests updating Godot.SourceGenerators, GodotSharp and GodotSharpEditor to the latest version. Looks like this action doesn't do anything, but it can mislead user into thinking they upgraded their environment to the latest version.

Adding IsImplicitlyDefined should prevent IDE from changing versions of these packages.

Screenshots

Before:

After:

2. Restore in Godot project fails when Central Package Management enabled

When using CPM with Godot, restore fails with error:

/path/cpm-test/CPM Test.csproj : error NU1008: Projects that use central package version management should not define the version on the PackageReference items but on the PackageVersion items: Godot.SourceGenerators;GodotSharp;GodotSharpEditor.

Example repository

With IsImplicitlyDefined="true", NuGet will not try to manage the SDK packages, resolving this error.

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This change is backwards compatible and should not break anything in existing projects. However, since IsImplicitlyDefined is not properly documented, I’d appreciate it if someone more knowledgeable in MSBuild could ensure that nothing will break unexpectedly.

What i found about IsImplicitlyDefined:

NuGet/Home#13529
https://github.com/dotnet/sdk/pull/43151/files#r1746148520

[raulsntos]

Thanks for contributing to the .NET module.

I'm not very familiar with this MSBuild property and, as you mention, it seems to be undocumented. However, the provided links about it were very helpful, and it seems harmless.

I tested this in Visual Studio and using the .NET CLI (dotnet list package --outdated) and it seems to works as described, so it looks good to me.

[Repiteo]

Thanks! Congratulations on your first merged contribution! 🎉