The core of the issue was that `sculpt_flag` was used by three different enums (`eGP_Sculpt_Flag`, `eGP_Sculpt_Mode_Flag`, and `eBrushFlags`). This resulted in the flag getting overriden because `ENUM_OPERATORS` expected the maximum value of `eGP_Sculpt_Flag` to be `(1 << 3)` which it wasn't.
The `sculpt_flag` was exposed through python as `"direction"`.
In the UI this meant that it was effectively used as `brush.direction`. This fix replaces `brush.gpencil_settings.direction` with `brush.direction`.
It also makes sure `sculpt_flag` is only ever used with values from `eGP_Sculpt_Flag`.
Pull Request: https://projects.blender.org/blender/blender/pulls/119373
998514af7b