Use conditions not cases in vec_case_when()

[DavisVaughan]

This now seems obvious to me

• vec_if_else(condition, true, false, ...)
• vec_case_when(conditions, values, ...)
• vec_replace_when(x, conditions, values, ...)
• vec_pany(...) and vec_pall(...) would take condition vectors Implement vec_pany() and vec_pall() #1675
• We internally call all of these logical condition vectors