libretro: support bin/cue games format

[soredake]

Describe the bug

I want to have support for copying multiple files (bin) and selecting main file (cue or iso) automatically.

It needs new installer task, open the file picker (and allow selecting multiple files), when files are copied to destination task will automatically select automatically or manual, iso as main file if only one file is copied, or cue file if multiple files are copied, and set main_file to the (automatically?) selected mine file.

something like this:

files:
- files: N/A:Please select the Dreamcast image file
game:
  core: reicast
  main_file: main_file
installer:
- copy_and_select:
    dst: $GAMEDIR
    description: "Please select the your files, iso or bin/cue"
    src: files

Expected behavior

Please describe the behavior you are expecting.

Current behavior

What is the current behavior?

Steps to reproduce

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System information

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