go/types: use function name position for init errors

go/types: use function name position for init errors

This seems more sensible than the func keyword. With this change,
go/types uses the same error position as types2 and we can narrow
the error tolerance a bit.

(The types2 change doesn't change its position, but it makes the
code clearer and symmetric to go/types.)

Change-Id: Iedea7c80caa7239a4343c8748cb779ec545e84d5
Reviewed-on: https://go-review.googlesource.com/c/go/+/427775
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>