go/printer: revert "do not treat comments inside a ast.Decl as godoc"

go/printer: revert "do not treat comments inside a ast.Decl as godoc"

This reverts commit CL 609077.

Reason for revert: it turned out to also introduce a change to the
formatting as described in issue #69382, which wasn't intended.

For #69382.

Change-Id: Id8f36e5503e63e7586c8afe7c7d3dc25fd56ed94
Reviewed-on: https://go-review.googlesource.com/c/go/+/612137
Reviewed-by: Christian Höppner <hoeppi@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>