give steps option to produce sparse output

[EmilHvitfeldt]

Extracted from tidymodels/planning#29

• step_count()
• step_date()
• step_dummy() #1392
• step_dummy_extract()
• step_dummy_multi_choice()
• step_holiday()
• step_indicate_na()
• step_ordinalscore()
• step_regex()
• step_intercept()
• step_interact()