Fallback icon pack

[jm355]

Is your feature request related to a problem? Please describe.
I'm using an icon pack that is missing a lot of icons for apps I use.

Describe the solution you'd like
I'd like to be able to set another icon pack as the fallback for missing icons before using system icons

Describe alternatives you've considered, or that are already available within KISS
Some kind of tool to merge icon packs would work, idk if one exists. Kind of like iconeration

Additional context
n/a

Would you be able to contribute code?
Maybe, I'm not super familiar with android dev, but with some tips I could probably figure it out

[EchedelleLR]

Thank you for reporting. Also looking for this.

[github-actions]

This issue has been closed automatically. Please see #1688 for details.
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