* establish basic event loop for workers
* make "self.close()" inside worker
* remove "runWorkerMessageLoop() - instead manually call global function
in Rust when message arrives. This is done in preparation for structured clone
* refactor "WorkerChannel" and use distinct structs for internal
and external channels; "WorkerChannelsInternal" and "WorkerHandle"
* move "State.worker_channels_internal" to "Worker.internal_channels"
* add "WorkerEvent" enum for child->host communication;
currently "Message(Buf)" and "Error(ErrBox)" variants are supported
* add tests for nested workers
* add tests for worker throwing error on startup
Ref #3712. This change allowed the deno_typescript crate to reference
cli/js/lib.deno_runtime.d.ts which breaks "cargo package". We intend to
reintroduce a revised version of this patch later once "cargo
package" is working and tested.
This reverts commit 737ab94ea1.
