Remove some minor hot spots in scheduling and executing Worker API actions. - Don't create JVM options for a legacy worker action until needed. - Don't create the parameters of a legacy worker action more than once. - Improve inference of an isolated object's parameter type.
Also restructure to decouple the different kinds of worker action specs, to allow the different specs to carry different information and also to make clearer what state a given stage of the execution pipeline expects the spec and its parameters to be in.