Unblock select2 suggestion widget in subwidgets for complex fields for target platform >= 5.7.3

In Studio :

• I choose target platform 5.7.3
• I create a doctype
• In my schema I set a complex field having a subfield, multivalued, of String type
• In my layout I drag and drop the complex field
• I click on the subwidget icon
• In the subfield the multiple user suggestion is not available although the use of select2 widgets should allow this