inspector: add inspector.waitForDebugger()

This method blocks current node process until a client sends
Runtime.runifWaitingForDebugger.

It can be useful when we need to report inspector.url() before
waiting for connection:
```
inspector.open(0, undefined, false);
fs.writeFileSync(someFileName, inspector.url());
inspector.waitForDebugger();
```

PR-URL: https://github.com/nodejs/node/pull/28453


Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>