Autocompletion: automatically insert constant values when properties are autocompleted

[FALLAI-Denis]

Describe the solution you would like

A schema can declare properties associated with a constant value.

We would like the constant value associated with a property to be automatically inserted at the same time that this property is autocompleted.

[FALLAI-Denis]

The automatic insertion of value during autocompletion could also concern:

• the "default" value
• the "enum" value when it is unique