Increase the number of buttons

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Is your feature request related to a problem? Please describe.

My Game Controller is Fiydigi Vader 2 . It has four back buttons and two additional front buttons ("C" "Z") .
In the AntiMicoX 3.32, "Controller Mapping" didn't reserve their place . They can map Strings in a preemptive way ( Should I describe it this way, I have just contacted AntiMicroX, and I do not know the underlying logic, String, API or SDL2 ) .
"Options"--> "property"-->"buttons" can detect these 6 buttons, but cannot respond ( blue ) unless in a preemptive way .
The main page can also show them button 16～ button 21, as if they are eagerly waiting to map a keyboard letter。
How should I read the source code and modify it，detect --> respond --> map a letter。

### Describe the solution you'd like

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### Describe alternatives you've considered

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### Additional context

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