Generic "read line" function for scripting

[KockaAdmiralac]

Which component should be improved?

CLI

Describe your feature suggestion in more detail

For the Deltarune code viewer, I wanted to make our ExportCodeFormatted.csx script read the output directory from stdin. This didn't work, because UTMT's CLI does not expose a great way for me to do this:

• PromptChooseDirectory() requires the directory being chosen to exist (the script is creating the directory)
• Console.ReadLine() doesn't work, because the input is non-interactive (in GitHub Actions)
• PromptPath() and ReadLineWithFallback() are private

I think it would be useful if ReadLineWithFallback() and/or PromptPath() were exposed to the scripting environment.