Supporting `cwl:hints` in addition to `cwl:requirements` for input objects

This feature will be helpful to implement a full-featured platform with another platform that only supports CommandLineTool.

Here is a use case:

The [spec](https://www.commonwl.org/v1.2/CommandLineTool.html#Execution_concepts) allows us to implement platforms that only support the CommandLineTool.
> A workflow platform may choose to only implement the Command Line Tool Description part of the CWL specification.

One idea to implement a full-featured platform is to implement only the control of the steps and to delegate the executions of the CommandLineTool to other platforms that support CommandLineTool.

Thanks to the [`cwl:requirements`](https://www.commonwl.org/v1.2/Workflow.html#Requirements_and_hints), we can easily impelement an inheritance of `requirements`; just generating an input object with `cwl:requirements` and pass it to the other platform to execute CommandLineTool.

However, there are no official ways to override `hints`. It would be nice to support `cwl:hints` in addition to `cwl:requirements`.