Make sure suggested FEEL functions can be executed in forms

[barmac]

What should we do?

• Make sure all suggested functions can be evaluated (finish feat: implement round functions nikku/feelin#79)
• Establish a continuous test for suggested functions

We may need to provide Camunda extensions via a wrapper, or stop suggesting Camunda extensions in forms as they'd need to be provided separately.

Why should we do it?

Problem reported via https://camunda.slack.com/archives/C0693F1NFK5/p1728639145792559
Follow-up discussion https://camunda.slack.com/archives/GP70M0J6M/p1728641414950129

[Buckwich]

with camunda/feel-builtins#20 i prepared for this, with this change consumers can decide if they want to use the full set (camundaBuiltins) or without the camunda extensions (feelBuiltins).

There might still be issues as not all functions are supported by feelin (eg upcoming dmn specs like from json, not marked as camunda extension), but we could extend the extractor with a feelin check to test if they evaluate and have a feelinBuiltins set.