Add streaming support to GHC debug brick

This is accomplished by a new tracing module GHC.Debug.StreamedTrace that is able to produce results incrementally.

I tried out this patch but it doesn't appear finished.

• Not all the objects appear to be found (I searched for DynFlags and only 1 result was retained bu there are 3300 live)
• No visual indicator that a search is ongoing when the results are being streamed.
• If you attempt to start another query when a search is on-going then it just closes the dialog box and shows the keybindings.
• The "parents" field of Closure doesn't seem to be always populated, it wasn't immediately clear to me what the purpose of that was.

It does look like a good start though, but I'll make the 0.7 release without merging this.