Convert all solution files to .slnx format

Not renaming the `.sln.DotSettings` file, because JetBrains tools seem
to prefer it for team-wide settings even with `.slnx` solution files.

Author: stakx

Castle.Core.sln

@@ -0,0 +1,26 @@
+<Solution>
+  <Folder Name="/Castle Build/">
+    <File Path=".editorconfig" />
+    <File Path=".gitattributes" />
+    <File Path=".gitignore" />
+    <File Path="appveyor.yml" />
+    <File Path="build.cmd" />
+    <File Path="build.sh" />
+    <File Path="buildscripts/common.props" />
+    <File Path="CHANGELOG.md" />
+    <File Path="CONTRIBUTING.md" />
+    <File Path="LICENSE" />
+    <File Path="README.md" />
+  </Folder>
+  <Folder Name="/Castle Build/GitHub Actions/">
+    <File Path=".github/workflows/build.yml" />
+  </Folder>
+  <Folder Name="/Castle Services/">
+    <Project Path="src/Castle.Services.Logging.log4netIntegration/Castle.Services.Logging.log4netIntegration.csproj" />
+    <Project Path="src/Castle.Services.Logging.NLogIntegration/Castle.Services.Logging.NLogIntegration.csproj" />
+    <Project Path="src/Castle.Services.Logging.SerilogIntegration/Castle.Services.Logging.SerilogIntegration.csproj" />
+  </Folder>
+  <Project Path="src/Castle.Core.Tests.WeakNamed/Castle.Core.Tests.WeakNamed.csproj" />
+  <Project Path="src/Castle.Core.Tests/Castle.Core.Tests.csproj" />
+  <Project Path="src/Castle.Core/Castle.Core.csproj" />
+</Solution>

Castle.Core.slnx

@@ -21,7 +21,7 @@ echo ---------------------------
 echo Build
 echo ---------------------------
 
-dotnet build ./Castle.Core.sln --configuration Release --tl:off
+dotnet build ./Castle.Core.slnx --configuration Release --tl:off
 
 echo ---------------------------
 echo Running NET8.0 Tests

build.sh

@@ -26,7 +26,7 @@ SET Configuration=Release
 GOTO build
 
 :build
-dotnet build ./tools/Explicit.NuGet.Versions/Explicit.NuGet.Versions.sln
+dotnet build ./tools/Explicit.NuGet.Versions/Explicit.NuGet.Versions.slnx
 dotnet build --configuration %Configuration% || exit /b 1
 .\tools\Explicit.NuGet.Versions\build\nev.exe ".\build" "castle."
 GOTO test

buildscripts/build.cmd

@@ -0,0 +1,3 @@
+<Solution>
+  <Project Path="Explicit.NuGet.Versions.csproj" />
+</Solution>