Input type inference

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Please describe what you would like to see in this project

When the user does not provide a workflow input schema, the engine should automatically infer the type based on the expressions that use the input.

Please describe your use case

Writing workflows, and subworkflows (see #26 and #71) specifically require the user to write a great deal of boilerplate code. To make this effort easier, the user should not have to provide an input schema for the subworkflows. The main workflow can use this functionality too, but we should recommend still writing a schema for documentation purposes. Later on, the functionality can be extended to output the input schema as a starting point.

Additional context

The speculative input type inference requires that the expression language can do forward type inference, the reverse of the current Dendencies and Types function. An expression should be provided with an outcome type and it should be able to construct the type required to produce the desired input.