Add project restore files and NuGet cache for GsaViewer

- Created project.nuget.cache to store NuGet package cache information.
- Added project.packagespec.json to define project restore settings and dependencies.
- Included rider.project.restore.info for Rider IDE integration.

GsaEditor/bin/Debug/net8.0/GsaEditor.runtimeconfig.json

@@ -0,0 +1,13 @@
+{
+  "runtimeOptions": {
+    "tfm": "net8.0",
+    "framework": {
+      "name": "Microsoft.NETCore.App",
+      "version": "8.0.0"
+    },
+    "configProperties": {
+      "System.Runtime.InteropServices.BuiltInComInterop.IsSupported": true,
+      "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": false
+    }
+  }
+}