runtime: disallow closing bubbled chans from outside bubble
A chan created within a synctest bubble may not be
operated on from outside the bubble.
We panicked on send and receive, but not close.
Panic on close as well.
For #67434
Change-Id: I98d39e0cf7baa1a679aca1fb325453d69c535308
Reviewed-on: https://go-review.googlesource.com/c/go/+/671960
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Damien Neil <dneil@google.com>