chore: fix ReferenceBuilder path handling for VS Debug and dotnet run

[guitarrapc]

tl;dr;

Current ReferenceBuilder output path is working for VS Debug run, but not for dotnet run --project sandbox\ReferenceBuilder\ReferenceBuilder.csproj. This PR fix to run on both.

$ dotnet run --project sandbox\ReferenceBuilder\ReferenceBuilder.csproj
Unhandled exception. System.IO.DirectoryNotFoundException: Could not find a part of the path 'C:\docs\reference_factory.md'.
   at Microsoft.Win32.SafeHandles.SafeFileHandle.CreateFile(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options)
   at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
   at System.IO.File.OpenHandle(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize)
   at System.IO.File.WriteToFile(String path, FileMode mode, String contents, Encoding encoding)
   at Program.<Main>$(String[] args) in C:\github\cysharp\R3\sandbox\ReferenceBuilder\Program.cs:line 6

TODO

• Run on VS Debug Run

(1175, 1268)
(1300, 1585)

• Run on dotnet run

$ dotnet run --project sandbox\ReferenceBuilder\ReferenceBuilder.csproj
(1175, 1268)
(1300, 1585)