[release-branch.go1.18] doc: update go_spec.html with latest changes

Generated at 2022-03-14 14:50 (EDT) with:

	git fetch
	git checkout origin/master -- doc/go_spec.html

This includes spec changes up to CL 391754.

Fixes #51532.

Change-Id: I2c23d764ffa33f24647cd2a4060268c1500f6f99
Reviewed-on: https://go-review.googlesource.com/c/go/+/392674


Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>