Ignore sln files and csproj files in the vendor directory (#5663)

.gitignore

@@ -359,4 +359,9 @@ build/
 # Default Assets restore directory
 .assets
 
-CMakeUserPresets.json
+CMakeUserPresets.json
+
+# Disable VS solution files and csproj files because they pollute the VS experience.
+**/vendor/**/*.sln
+**/vendor/**/*.csproj
+