prints function
Matches a Function that prints text that matches matcher.
matcher may be a String or a Matcher.
If the function this runs against returns a Future, all text printed by the function (using Zone scoping) until that Future completes is matched.
This only tracks text printed using the print function.
This returns an AsyncMatcher, so expect won't complete until the matched
function does.
Implementation
Matcher prints(matcher) => _Prints(wrapMatcher(matcher));