When the brush refactor project was in progress, the "Fake Neighbors"
feature used exclusively by the Pose brush was made more explicit.
However, the migration missed the usage of this data in the `flood_fill`
APIs.
This resulted in the option not affected unconnected topology islands
except when the Pose Origin Offset was non zero and using the Topology
mode of the brush.
To fix this, this commit updates the flood_fill APIs to take in the
pre-calculated fake neighbor data and use it when traversing connected
vertices and applying weights.
Pull Request: https://projects.blender.org/blender/blender/pulls/132610
72180241c1