feat(feel): add number feel entry

[pinussilvestrus]

Related to bpmn-io/form-js#653

Adds an optional FEEL number field entry. This enabled us to create number properties with FEEL support (e.g. min, max, minLength, maxLength in form-js, bpmn-io/form-js#668).

[pinussilvestrus]

I created a demo in form-js for the 4 mentioned validation properties: https://demo-653-min-max-feel--camunda-form-playground.netlify.app/

[pinussilvestrus]

I found out that decimal numbers are not working anymore in the optional FEEL number field. I'll investigate.

[nikku]

Thanks @pinussilvestrus. I looked into the demo you provided and found one glitch: Entering a . breaks the editor focus (moves the cursor):

Expected behavior:

• character is disallowed or character is passed, but an error message (invalid format) is shown

[pinussilvestrus]

@nikku I decided to simply re-using the existing NumberField so we have a consistent behavior between FEEL and non-FEEL number entries. I'm not sure what's the expected behavior, but it should work the same as before now (without jumping cursor).

[nikku]

Works for me now.