Add "argsExpansion" debug property to launch.json schema

[int19h]

This was added to debugpy in microsoft/debugpy#230 to resolve a specific issue on the extension side. But it's generic enough to be broadly useful, so we should expose it to the users.

[ericsnowcurrently]

Also see microsoft/debugpy#156 and #11562.

[ericsnowcurrently]

Pavel Minaev (@int19h), we also need to add "argsExpansion"=trueto our launch config for tests, right?

[int19h]

"argsExpansion": false, I think.

[int19h]

Slight correction: it is "none" or "shell", not a boolean. So tests should be using "none".