Draft: Fix #746 (CLI) Auto-detect Core when -L isn't present

[zig-for]

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Description

This allows Retroarch to attempt to pick the proper core when loading. Windows already does this on drag and drop.

The PR as is doesn't handle missing cores, nor does it delegate to the frontend if there's multiple possible cores. Happy to put work towards that if there's a desire for this to go in. The main desire is to try to push for a "good" solution even if no perfect solution exists (I'd rather a happy path of being able to easily set file extensions associated with RA to do the right thing, then give up on every case just because some cases are hard to handle).

To repeat - as is, the PR is not ready, just looking for direction on both implementation and probability of acceptance later

EDIT: Additional changes:

• Always allows downloading cores when suggesting cores
• Fixes bug that caused cancelling "Core Downloader" to pop the entire menu stack if run from anywhere but "Online Updater"
• The core download menu is now filtered when appropriate

Current bugs:

• [ ] When backing out from the content suggester, the main menu on the left isn't scrolled properly
• [ ] Suggested cores don't show licenses (is this desired? I kind of like the slim, clean look)

Related Issues

https://github.com/libretro/RetroArch/issues/746 https://github.com/libretro/RetroArch/issues/9275 https://forums.libretro.com/t/autodetect-core-when-opening-a-rom-file/1863 https://github.com/libretro/RetroArch/issues/1704 https://github.com/libretro/RetroArch/issues/8557

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