Add VisualServer methods to get the video adapter name and vendor

These methods can be used in scripts to retrieve the OpenGL
`GL_RENDERER` and `GL_VENDOR` strings (respectively).

This closes #28404.

servers/visual_server.h

@@ -1017,6 +1017,8 @@ public:
 	};
 
 	virtual int get_render_info(RenderInfo p_info) = 0;
+	virtual String get_video_adapter_name() const = 0;
+	virtual String get_video_adapter_vendor() const = 0;
 
 	/* Materials for 2D on 3D */