feat(forms): support multiple-select dropdowns in Fields plugin questions

[MyvTsv]

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes !46141
• In GLPI version 11, forms do not support questions with custom multiple-choice dropdown lists. It was difficult to use multiple-choice drop-down lists in a form because this could cause compatibility issues.

However, drop-down lists with multiple-choice options are fully supported by forms in GLPI 12. This PR adapts the plugin to ensure that fields of this type are fully compatible.