Filesystem autocompletion should be case insensitive on Windows/macOS

[Meakk]

Describe the bug
When pressing TAB to autocomplete a file path in the console, the suggested paths should take into account the case sensitivity of the OS.

To Reproduce
Steps to reproduce the behavior:

Let's say we have two folders C:\ABC and C:\abc

1. Run f3d
2. Open the console (ESC)
3. Type add_file C:\a
4. Only C:\abc shows up

Expected behavior
Both folders should appear in the suggestion

System Information:

• OS: Windows (but macOS too probably)
• GPU and GPU driver: not relevant

F3D Information
Paste the content of f3d --version or f3d-console.exe --version on Windows: 3.3.0

Additional context
We should also take into account Linux filesystems with case sensitivity turned off ideally.

[skusel]

I would be happy to work on this.

[mwestphal]

Nice to see you are back! Assigned :)