Support await from debug console

I can't use `await` from the debug console in vscode. It shows the following error:
```
await 1
SyntaxError: await is only valid in async functions, async generators and modules
```

But this works from the debug console in firefox.

It would be really nice if we could use await expressions in vscode too, as without them it's not so easy to inspect results of async functions.

Start at the VS Code debug console handling and compare its evaluation behavior with Firefox's debug console, where `await 1` works. Confirm the current SyntaxError, then verify that await expressions and async-function results can be inspected in VS Code without that error.

Written by the indexing model from the issue text.