file_icons: Fall back to the default icon theme for icons (#23196)

This PR updates the various `FileIcons` methods to fall back to the
default icon theme if the active icon theme does not have the desired
icon.

Release Notes:

- N/A
a8526d9143Marshall Bowers committed on 1/15/2025, 10:06:20 PM· committed by GitHubparent904b367
2 files changedLine totals unavailable