The debug console will now show an indicator when it's unopened and
there's unread messages.

`NewSessionModal` attempts to resolve debug configurations before using
the config to start debugging. This allows users to use zed's task
variables in the modal prompt.

I had to invert tasks_ui dependency on debugger_ui so `NewSessionModal`
could get the correct `TaskContexts` by calling tasks_ui functions. A
consequence of this workspace has a new event `ShowAttachModal` that I'm
not a big fan of. @osiewicz if you have time could you please take a
look to see if there's a way around adding the event. I'm open to pair
on it too.

Release Notes:

- N/A