[Autocomplete] Fix handling of associated properties in DQL joins

[HugoSEIGLE]

Q	A
Bug fix?	yes
New feature?	no
Issues	Fix #2370
License	MIT

Changes:

• The alias generation logic has been improved to correctly handle nested associations and avoid alias collisions.
• The code was modified to ensure that the parent entity is correctly accounted for when generating aliases, which helps prevent issues in complex joins with multiple associated entities.
• A check was added to verify the existence of a parent property before using it as part of the alias. This prevents logical errors in cases where the parent entity is not directly involved in the join.