go/printer, gofmt: handle raw string literals containing newlines better

A raw string containing newlines breaks whatever columns structure
has been established so far. Recognize the situation and force a
new section of alignment with the first line break seen after the
the raw string.

Applied gofmt to src and misc.

Fixes #9064.

Change-Id: I961e94b529b1fd421908311f366b113e2ec9b7f0
Reviewed-on: https://go-review.googlesource.com/105040


Reviewed-by: Matthew Dempsky <mdempsky@google.com>