fix stepaction param default value referencing other param

[waveywaves]

• multipass default value substitution: one for non referenced default values, another one for parameter references in default values
• add validation to ensure parameters referenced in default values are defined before use
• substitute default values of parameters with referenced parameter values if necessary
• update replacementsFromStepResults to only process step result references
• add comments which highlight order of hydration of parameters
• add tests for replacementsFromStepResults, validateDefaultParameterReferences
• add example for parameter references in default values of step action parameters

Changes

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