migrate to new solution format

Author: w8tcha

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
           dotnet-version: ${{ matrix.dotnet-version }}
       - name: Install dependencies
         working-directory: ./
-        run: dotnet restore ./YAF.SampleApp.sln
+        run: dotnet restore ./YAF.SampleApp.slnx
       - name: Build
         working-directory: ./
-        run: dotnet build ./YAF.SampleApp.sln
+        run: dotnet build ./YAF.SampleApp.slnx

YAF.SampleApp.sln

@@ -0,0 +1,6 @@
+<Solution>
+  <Folder Name="/Solution Items/">
+    <File Path=".editorconfig" />
+  </Folder>
+  <Project Path="YAF.SampleApp/YAF.SampleApp.csproj" />
+</Solution>