Use Halley's method in LambertW for cubic convergence.    - Change stopping condition to relative error.    - Limit number of iterations to a 100. For some values of x in different backends, the iterations converge really slowly and can timeout the test. 100 was heuristically chosen as an upper bound by sweeping through values and scanning what the relative error of the computation was.
Use Halley's method in LambertW for cubic convergence.
   - Change stopping condition to relative error.
   - Limit number of iterations to a 100. For some values of x in different backends, the iterations converge really slowly and can timeout the test. 100 was heuristically chosen as an upper bound by sweeping through values and scanning what the relative error of the computation was.

PiperOrigin-RevId: 312131423

tensorflow/probability,tensorflow/probability