VS: Emit UTF-8 BOM for generated solution files

We write UTF-8-encoded content to the `.sln` files, so tell VS to read
them as such.

Fixes: #19594

Source/cmGlobalVisualStudioGenerator.cxx

@@ -104,6 +104,9 @@ const char* cmGlobalVisualStudioGenerator::GetIDEVersion() const
 
 void cmGlobalVisualStudioGenerator::WriteSLNHeader(std::ostream& fout)
 {
+  char utf8bom[] = { char(0xEF), char(0xBB), char(0xBF) };
+  fout.write(utf8bom, 3);
+
   switch (this->Version) {
     case cmGlobalVisualStudioGenerator::VS9:
       fout << "Microsoft Visual Studio Solution File, Format Version 10.00\n";