behaviour of the multiple select

[Garfield-fr]

Describe the issue
When you add the "uniqueItems" option to a select type, it turns into a single menu with several values. This is not the expected behavior.

To Reproduce
Steps to reproduce the behavior:

1. Add "uniqueItems": true on jsonschema
2. Check field form

Expected behavior
When adding the "uniqueItems" option, the field must not change its shape. It must remain a simple menu. It is only at the validation level that it must behave.

Software version
ng-core: 1.14.2