Fix autocompletion for enum members in the core classes

[Chaosus]

My attempt to fix #84509

PS: Also fixed the completion of inner classes (where only the enums or subclasses should be returned)

[Calinou]

Tested locally, it works as expected. Needs a rebase before it can be merged.

simplescreenrecorder-2024-02-05_23.51.36.mp4

[Chaosus]

Rebased*.

[akien-mga]

Thanks!