rm unused require from signal-generator model
Ensure builtin properties always have descriptions

IS [#63728770]

The sensor model uses property descriptions to "freeze" certain builtin properties.
Allow playbackSupport to be optional

IS [#63728770]

Mixing playbackSupport into a model causes the model's tick method to be called by an internal timer. However, this is not appropriate for models which "tick" on the receipt of external input, such as the sensor models. Because however these models can use every other part of the labModelerMixin, make just playbackSupport optional.
use LabModelerMixin to rm code from sensor model

IS [#63728770]