"Insert single proposals automatically" does not work in 2024-06

I noticed this issue when updating from 2020-06 to 2024-06

In Eclipse 2020-06, typing ``sysout`` and pressing Ctrl + Enter autocompletes it to ``System.out.println()``, when "Insert single proposals automatically" is enabled. In 2024-06, it doesn't autocomplete and the option has no effect.

The option:

Eclipse 2020-06: After turning on the option, it autocompletes

https://github.com/user-attachments/assets/b3ba573f-81eb-44bb-9f01-cb2247141060

Eclipse 2024-06: It just opens the menu

https://github.com/user-attachments/assets/9da439ce-49ec-4230-9012-41f0c6e8116d

Start by reproducing the issue in Eclipse 2024-06 with "Insert single proposals automatically" enabled, typing `sysout`, and pressing Ctrl+Enter; compare the result with Eclipse 2020-06. Trace the content-assist path responsible for this preference. Done means the single `System.out.println()` proposal is inserted automatically again.

Written by the indexing model from the issue text.