doc/go1.16: fill in Go 1.16 release note TODOs using relnote
doc/go1.16: fill in Go 1.16 release note TODOs using relnote

The additions were generated using golang.org/x/build/cmd/relnote
at CL 272907. It was modified to find previously-missed entries
by querying the Gerrit API in addition to the maintner corpus.

For #40700.
Updates #41849.

Change-Id: If575984fe40e0133ad5e8fc5411ea5063457250d
Reviewed-on: https://go-review.googlesource.com/c/go/+/272871
Trust: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>

CAFxX/go,cloudflare/go,CAFxX/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,nawawi/go,CAFxX/go,golang/go,golang/go,CAFxX/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,golang/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,golang/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,nawawi/go,golang/go