Fix NuGet fallback folder packages

[raulsntos]

• Creates a Godot.Offline.Config file to configurate NuGet with Godot's fallback folder. This is easier because now we can assume we can override the entire file since user config will likely be in the default NuGet.Config file or an additional *.config file.
  • See https://docs.microsoft.com/en-us/nuget/consume-packages/configuring-nuget-behavior#additional-user-wide-configuration
• Ensure the NuGet fallback folder is created at the same time it is added to the NuGet configuration so future builds don't fail.
  • Fixes Launching godot 4.0 (master) with mono breaks later godot+mono build attempts #44532
• Add GodotSharp and GodotSharpEditor packages to the fallback folder.
• Add .nupkg.metadata file to packages in fallback folder.
  • This file seems to be necessary, without it building projects offline was failing to resolve the packages for me with error NU1100. I could not find version 2 of the metadata file spec but I copied what nuget add -Expand creates.

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⚠️ I'm still unable to resolve the Godot.SourceGenerators package using the fallback folder and it seems to be related to using a floating version because using the exact package version works:

godot/modules/mono/editor/Godot.NET.Sdk/Godot.NET.Sdk/Sdk/Sdk.targets

Line 20 in 5803a1d

<PackageReference Include="Godot.SourceGenerators" Version="$(PackageFloatingVersion_Godot)" />

Here's the full error I get:

Build FAILED.

       "/media/raulsntos/Data/GodotProjects/TestProject/TestProject.sln" (Restore target) (1) ->
       (Restore target) -> 
         /media/raulsntos/Data/GodotProjects/TestProject/TestProject.csproj : error NU1100: Unable to resolve 'Godot.SourceGenerators (>= 4.0.0-0)' for 'net6.0'. [/media/raulsntos/Data/GodotProjects/TestProject/TestProject.sln]

    0 Warning(s)
    1 Error(s)

[neikeq]

⚠️ I'm still unable to resolve the Godot.SourceGenerators package using the fallback folder and it seems to be related to using a floating version because using the exact package version works:

But AFAIK this worked for you with the local NuGet source that's needed during development, right? I think we should probably create a local source instead of a fallback folder.

[raulsntos]

But AFAIK this worked for you with the local NuGet source that's needed during development, right?

Yeah, it works with a local source but not when it's a fallback folder. No idea why. This issue is the reason I'm keeping this as a draft.

I think we should probably create a local source instead of a fallback folder.

I don't really know what that implies, other than the difference in precedence. As described in the nuget.config documentation a source would be used after the fallback folder and in the order they are specified (but file sources before http sources). Since our local source would be a file source it would still be used before the nuget.org source which is an http source so I guess nothing would change.

[neikeq]

I meant that if it doesn't work with a fallback folder, but it does with a local source, then this class should be creating a local source instead and adding that to the config file.

[raulsntos]

The Godot.SourceGenerators is referenced using a floating version to avoid having to update Godot.NET.Sdk for every update of the source generators (see #55597 (comment)), but since we'll be removing the fallback folder in the future we could undo it and use the specific version number as a temporary solution for the few alphas/betas until we publish the packages to nuget.org.

[akien-mga]

Thanks!