Also make all AstVisitors consistently visit all the relevant parts
of ForOfStatement. PrettyPrinter no longer fares well, but given
how much desugaring happens to ForOf in the parser, any pretty-printed
view of it isn't going to be human readable. AstPrinter, on the other
hand, now gives a realistic view of what's been generated for for-of.

Review-Url: https://codereview.chromium.org/1968753004
Cr-Commit-Position: refs/heads/master@{#36215}