This is a conversion static method in both

• template class and
• interface marker class

CT, signed

  public static ContractId byId(codegen.ContractId<CT> genericForm)

As this method replaces ContractId.fromContractId, which isn't present for interface ContractId classes, that

• generated fromContractId should be deprecated, with a note pointing to the new byId method.

This idea came up in #14420 by @StephenOTT, for its symmetry with byKey. We can do this to fix the missing fromContractId with a more easily-accessible version, while also providing a prerequisite to getting rid of the ContractId class entirely as suggested by @cocreature, should we decide to do that, in the form of a method that would give generic-ContractId users access to the Exercises.