NuGet packaging of DesignTime DLL for F# provider

[xperiandri]

Added MSBuild target to ensure DesignTime DLL is included in NuGet package, working around F# SDK limitations with ProjectReference-based providers. Removed obsolete target for cleaning NuGet pack input and updated conditions for consistency.

[xperiandri]

@T-Gro, I discovered that the design-time DLL is no longer packaged into the NuGet package.
Could you confirm that this solution is the right way?

[Copilot]

Pull request overview

This PR adjusts NuGet packaging for the FSharp.Data.GraphQL.Client type provider so the *.DesignTime.dll is included in the produced package, working around limitations in the F# SDK/MSBuild packing flow when a runtime project references its design-time project via ProjectReference.

Changes:

• Adds a custom target hooked via TargetsForTfmSpecificContentInPackage to inject the DesignTime DLL into the package.
• Removes the previously-used RemoveUnnecessaryNuGetPackInput target and cleans up NuGet-related conditions for consistency.
• Updates ProjectReference / PackageReference conditions to use quoted $(IsNuGet) comparisons.

[github-actions]

Test Results

    3 files      3 suites   9m 58s ⏱️
  442 tests   437 ✅  5 💤 0 ❌
1 326 runs  1 311 ✅ 15 💤 0 ❌

Results for commit 56419ea.

[T-Gro]

@xperiandri : I will take a look and write here 👍

[T-Gro]

@xperiandri heads-up: the root cause behind this workaround is being fixed upstream in dotnet/fsharp#19979. PackageFSharpDesignTimeTools will again package a provider activated via <ProjectReference IsFSharpDesignTimeProvider="true"> on its own — resolved through the SDK's nearest-target-framework negotiation, with no reference build (so pack --no-build stays fine).

Once that ships in a future .NET SDK, the custom _IncludeDesignTimeDllInPackage target here can be removed: the stock gesture packages FSharp.Data.GraphQL.Client.DesignTime (and its sibling DLLs) into typeproviders/fsharp41/<tfm>/. Keep <FSharpToolsDirectory>typeproviders</FSharpToolsDirectory> to retain the current layout. No rush — please wait for the SDK that carries the fix before dropping the workaround.