swift234

[ASTPrinter] Funnel keyword printing through a common interface NFC

Start threading all keyword (and contextual keyword) printing through
printName, and add a new PrintNameContext for keywords.  For now we just
pass this through without changing behaviour.

Also add an operator<< for printing from the tok:: kind for keywords,
which makes it much more convenient for performing the required
callbacks.

rdar://problem/24292226