This fixes multiple issues:
- It does not make sense for the draw face set tool to have strength
applied as it is a binary operation (we can even consider not applying
the falloff curve). Using the strength value in this brush requires a
comparison with an arbitrary value.
- Strength in face sets relax mode was applied twice
- Fade was not clamped before the relax operation, so it may cause
problems when the brush strength is higher than 1.0