bug: file_picker uses unconventional system calls on linux + macos

[XavierChanth]

Which at_widget package you find issue with?

at_onboarding_flutter

On what platforms did you experience the issue?

MacOS

What version are you using?

v6.1.3

What happened?

All files in the picker are greyed out.

Steps to reproduce

Try to onboard from a more recent version of macOS using an existing keyFile.

Additional info

The best solution would be to remove file_picker entirely in favour of file_selector which is maintained by the flutter team. (we already use file_selector in at_backupkey_flutter so we should probably just stick to one package anyways)

https://github.com/miguelpruivo/flutter_file_picker/wiki/FAQ#q-when-using-file_picker-on-macos-or-linux-the-dialog-does-not-always-get-in-focus-so-there-is-an-extra-click-to-first-make-the-dialog-in-focus-before-you-can-actually-choose-a-file-can-you-make-the-dialog-focus-automatically-or-provide-a-better-user-experience--ux-in-general

Relevant log output

No response

Flutter analyze output

No response

Flutter doctor output

No response