C# GetApiVersionHash does not respect 'rename_symbols' config setting

[pixsperdavid]

When Config::rename_symbols is true, the generated API version check does not rename the call to the API version function, resulting in an uncompilable C# source file.

The CSharpWriter::write_abi_guard function likely needs to call self.converter().function_name_to_csharp_name(function, self.config().rename_symbols) in a similar way to CSharpWriter::write_function_declaration.