Typeset captured parts of steps differently based on type of captured value

We should typeset scenarios as steps so that we can do things like typeset captures depending on type.

For example, if a pattern captures text such as a string literal or a regex, it'd be nice to typeset the captured text in, say, monospace. This should probably be generalized so that the binding could set a style that gets translated into a typesetting decision.

• Decide on how bindings might suggest styles
• Rework formatting of scenarios