bug#38807: [Feature request]: Support lisp workers like web workers.

[HaiJun Zhang]

在 2020年1月2日 +0800 AM12:21，Eli Zaretskii <eliz@gnu.org>，写道：

Then these threads cannot really run Lisp at all, nor even directly
affect Lisp data. So in effect you want to be able to run threads
that don't enter the Lisp interpreter, nor modify any Lisp data.  

For web worker, they have different contexts. The following is from MDN(https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers):

workers run in another global context that is different from the current window. Thus, using the windowshortcut to get the current global scope (instead of self) within a Worker will return an error.

The worker context is represented by a DedicatedWorkerGlobalScope object in the case of dedicated workers (standard workers that are utilized by a single script; shared workers use SharedWorkerGlobalScope). A dedicated worker is only accessible from the script that first spawned it, whereas shared workers can be accessed from multiple scripts.