[REQ] Cross-platform build csharp-dotnet2 clients

Is your feature request related to a problem? Please describe.

Currently, the csharp-dotnet2 clients are not generated with a csproj inside it. Although it provides a Mono-based build script that downloads the nuget.exe, pulls the dependencies and builds the client library, this approach has the following problems:

• It's not the standard/recommended way of building .NET libraries
• It requires downloading an extra executable
• It requires a platform emulator
• It lacks support for Windows at the moment, as stated in the generated README file

Describe the solution you'd like

I'd like to purpose adding a csproj file to the generated csharp-dotnet2 client, so it can be used by the .NET SDK for:

• Building the code and generating the necessary DLLs in the specified target platform and runtimes (cross-platform).
• Automatically pull the specified dependencies without making it explicit.
• Generating and deploying a NuGet package without requiring a nuspec file.

Note: With this change, the packages.config and the compile-mono.sh are no longer necessary so they can also be removed from the generated clients.

Describe alternatives you've considered

N/A

Additional context

N/A

Locate the generator templates or output path for the csharp-dotnet2 client, then inspect the generated packages.config, compile-mono.sh, and README. Confirm how dependencies and build outputs are currently handled; done means generated clients include a usable csproj for cross-platform SDK builds and NuGet packaging, while obsolete files are removed.