Feature Request: Support `.slnx` Visual Studio solution format

[Therrania]

Description

The tool currently detects only legacy Visual Studio solution files (.sln).
It does not recognize the newer .slnx format, which causes csharp_set_workspace to fail when a workspace contains only a .slnx solution.

Expected behavior

• Detect and support .slnx files in addition to .sln
• Allow csharp_set_workspace to initialize the workspace using a .slnx solution

Why this is important

.slnx is the new XML-based solution format introduced in recent versions of Visual Studio and .NET, and its adoption is expected to grow. Supporting it ensures compatibility with modern .NET projects.

Reproduction

1. Create a workspace containing only MySolution.slnx
2. Call csharp_set_workspace
3. Workspace initialization fails

[nomenon]

yes, it is worth doing support .slnx