Improve validation support for NumberFieldEntry

[Skaiir]

Is your feature request related to a problem? Please describe

Currently, dealing with number fields can be a little bit confusing. While there is browser built-in validation for number fields, how it is displayed is browser dependent and at least in Firefox requires a hover on top of the field, which is pretty hard to find.

I don't think there exists a way to pipe the validation errors through to the UI via code (I could be wrong), though I know that via CSS we can at least apply some styling rules if the field is invalid, this might be useful. But in practice, I'd still rather have a similar validation experience as with the regular text fields.

Describe the solution you'd like

Allow the supplying of a validation function for the NumberFieldEntry component, mirroring how it is done for TextFieldEntry.

Describe alternatives you've considered

Rely solely on browser default validation, unfortunately, the way browsers do this lacks a bit of clarity

Additional context

Initial comment that shows the confusion people experience with this: bpmn-io/form-js#490 (review)

@nikku @philippfromme I'm happy to implement this myself, if you think this is a positive addition.

[philippfromme]

I think we should ignore the browser validation as it's essentially useless. Would be great to have an attribute like novalidate for number inputs.

We should

1. be able to add a validate function to a number field (similar to the text field https://github.com/bpmn-io/properties-panel/blob/main/src/components/entries/TextField.js#L99)
2. show validation errors below the number field
3. only commit if valid