go/format: skip go/ast's object resolution

Just like https://golang.org/cl/401454 removed the work from gofmt for a
nice ~5% speed-up in the default case, we can also use the option in the
equivalent go/format for programs which use it rather than gofmt,
as go/format makes no use of objects either.

No benchmark numbers as we already measured the ~5% speed-up with gofmt
in the other CL linked above.

See #46485.

Change-Id: Icbf98e6d46a616081314e2faa13f1dfade3bbaef
Reviewed-on: https://go-review.googlesource.com/c/go/+/401474
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/go/format/format.go

@@ -38,7 +38,7 @@ const (
 
 var config = printer.Config{Mode: printerMode, Tabwidth: tabWidth}
 
-const parserMode = parser.ParseComments
+const parserMode = parser.ParseComments | parser.SkipObjectResolution
 
 // Node formats node in canonical gofmt style and writes the result to dst.
 //