`fixedpoints` based on root finding

**Describe the feature you'd like to have** I'd like to suggest making the `fixedpoints` method from ChaosTools.jl available in Attractors.jl. This would allow finding attractors and edge states also via root finding, in addition to the current ways (via proximity, recurrence, featurizing). I would assume that for systems with fixed points this can be the most efficient way?