Fix - Use translated itemtype name for reservation item select groups

[RomainLvr]

Checklist before requesting a review

Please delete options that are not relevant.

• 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 complete Feat/reservation question #36 & fixes !39540
• Here is a brief description of what this PR does

The reservation item picker (Select2) grouped results using the raw PHP itemtype class name instead of its translated display name. This was invisible for core itemtypes like Computer or Monitor, but for custom assets it exposed the full namespace, e.g. Glpi\CustomAsset\TestcustomassetAsset instead of Test custom asset.

Screenshots (if appropriate):

Before

After