The UpdateSequenceGenerator class introduced in SERVER-29939 is parameterized by

1. A set of field names to use in the created document,
2. A maximum depth for nested subdocuments and arrays, and
3. A maximum length for array values.

may.hoque had the idea to bundle these options together in another class so that we didn't need to have every function take these constraints as threee separate parameters. Additionally, we should add the following additional parameters:

1. A floating-point value between 0 and 1 (inclusion) to indicate the probability with which to generate a $set with a scalar value,
2. A floating-point value between 0 and 1 (inclusion) to indicate the probability with which to generate a $set with a subdocument, and
3. A floating-point value between 0 and 1 (inclusion) to indicate the probability with which to generate a $set with an array value.

Subtracting the sum of the above probabilities from 1 should yield a floating-point value between 0 and 1 (inclusive) to indicate the probability with which to generate an $unset.

Note: Until SERVER-28777 is implemented, multiInitialSyncApply_noAbort() will continue to use the 3.4 update codepath. The work described in this ticket serves as a workaround for SERVER-29944 (specifically by using probabilityOfArray=0) to avoid idempotency issues related to the handling of "blocking elements" / "non-viable paths" in the 3.4 update codepath.