net: enable most tests on wasip1 and js

net: enable most tests on wasip1 and js

To get them to pass, implement more fake syscalls.
To make those syscalls easier to reason about, replace
the use of sync.Cond with selectable channels.

Fixes #59718.
Fixes #50216.

Change-Id: I135a6656f5c48f0e5c43dc4d4bcbdb48ee5535d2
Reviewed-on: https://go-review.googlesource.com/c/go/+/526117
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Achille Roussel <achille.roussel@gmail.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>