Select default compiler should include the currently selected compiler if it is not listed elsewhere

Environment

In this discussion, a user is trying to configure a compiler that is installed by extracting a zip folder. The compiler is not in any of the paths we know about, but they managed to set it another way. If they run the Select Default Compiler or Select IntelliSense Configuration commands, the currently selected compiler does not appear in the list because it's not one we've scanned ourselves. We should include the currently selected compiler in the list if it is not already present in the drop down, or maybe just always show the currently selected compiler at the top of the list.

#12069

Bug Summary and Steps to Reproduce

• Install Mingw to c:\folderWithRandomName
• Set this compiler in c_cpp_properties.json
• Run the Select IntelliSense Configuration or the Select Default Compiler command

Notice that the currently selected compiler is not in the list. If it's the currently selected compiler (and it's valid), we should show it in the list.

Configuration and Logs

n/a

Other Extensions

No response

Additional context

No response