[dotnet] Migrate solution file to new .slnx format (#16638)

Co-authored-by: Nikolay Borisenko <[email protected]>

Author: RenderMichael

.gitattributes

@@ -10,6 +10,6 @@
 *.xml    text
 
 *.csproj text merge=union
-*.sln    text merge=union eol=crlf
+*.slnx    text merge=union eol=crlf
 
 *.docx   diff=astextplain

dotnet/Selenium.sln

@@ -0,0 +1,16 @@
+<Solution>
+  <Folder Name="/src/">
+    <Project Path="src/support/Selenium.WebDriver.Support.csproj" />
+    <Project Path="src/webdriver/Selenium.WebDriver.csproj" />
+  </Folder>
+  <Folder Name="/test/">
+    <Project Path="test/chrome/Selenium.WebDriver.Chrome.Tests.csproj" />
+    <Project Path="test/common/Selenium.WebDriver.Common.Tests.csproj" />
+    <Project Path="test/edge/Selenium.WebDriver.Edge.Tests.csproj" />
+    <Project Path="test/firefox/Selenium.WebDriver.Firefox.Tests.csproj" />
+    <Project Path="test/ie/Selenium.WebDriver.IE.Tests.csproj" />
+    <Project Path="test/remote/Selenium.WebDriver.Remote.Tests.csproj" />
+    <Project Path="test/safari/Selenium.WebDriver.Safari.Tests.csproj" />
+    <Project Path="test/support/Selenium.WebDriver.Support.Tests.csproj" />
+  </Folder>
+</Solution>

dotnet/Selenium.slnx

@@ -0,0 +1,6 @@
+<Solution>
+  <Folder Name="/Solution Items/">
+    <File Path="generator_settings_template.json" />
+  </Folder>
+  <Project Path="src/generator/DevToolsGenerator.csproj" />
+</Solution>