This makes the format code use the AST that is already cached on the file to do
the formatting. It also moves the core format code into the source directory.
Change-Id: Iaa79169708e92525cce326ea094ab98144fe1011
Reviewed-on: https://go-review.googlesource.com/c/148198
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
