Custom formatters for Slider/DragValue etc

[AlexApps99]

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

I'm making a debugger GUI for a project I'm working on, and I'd like to select an address from a DragValue.
However, it's conventional to notate addresses in zero-padded hexadecimal, rather than decimal.

Describe the solution you'd like
There should be some way to specify custom formatting on a number. Ideally this should be flexible so users can do whatever they want, like using Chinese numerals, base 12, or whatever.
This could be implemented with a function that takes a closure to format it, or it could be done by having a custom implementation of Display on Numeric.

Describe alternatives you've considered

We could also just have a flag for hexadecimal/pad length etc but that's probably not worth the complexity

Additional context

[emilk]

I think adding a custom formatting closure makes sense (similar to recent PR:s on Plot: #1130 and #934)