Brush directions are dynamic, the enum can have different options
depending on brush type. This commit manually extracts the options.
The labels use the "Brush" translation context, to disambiguate
"Deflate", the operation, with the compression algorithm.
Also `smooth_direction_items` is moved inside
`rna_Brush_direction_itemf()`, since it is used only there, same as
the other brush direction items.
Reported by Ye Gui in #43295.
Pull Request: https://projects.blender.org/blender/blender/pulls/148081
8bf46781b0