runtime,internal/poll: move websocket handling out of the runtime on Windows
On Windows, the netpoll is currently coupled with the websocket usage
in the internal/poll package.
This CL moves the websocket handling out of the runtime and puts it into
the internal/poll package, which already contains most of the async I/O
logic for websockets.
This is a good refactor per se, as the Go runtime shouldn't know about
websockets. In addition, it will make it easier (in a future CL) to only
load ws2_32.dll when the Go program actually uses websockets.
Change-Id: Ic820872cf9bdbbf092505ed7f7504edb6687735e
Reviewed-on: https://go-review.googlesource.com/c/go/+/556936
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Bryan Mills <bcmills@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>