Revisit Layer.output_signature:   - Tighten current test; clarify it only covers layers without weights.   - Flag need for defined behavior/test for layers with weights.
Revisit Layer.output_signature:
  - Tighten current test; clarify it only covers layers without weights.
  - Flag need for defined behavior/test for layers with weights.

PiperOrigin-RevId: 338775980

google/trax,google/trax