cmd/go: gofmt alldocs.go

cmd/go: gofmt alldocs.go

[This CL is part of a sequence implementing the proposal #51082.
The design doc is at https://go.dev/s/godocfmt-design.]

Reformat alldocs.go using the new doc comment formatter.

This file is so large it gets its own gofmt CL.

For #51082.

Change-Id: Ie14cf1aad776e6f4180d88245d05a86e5fb6a3b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/384267
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>