Track running processes in debugger (#833)

* track running processes in debugger

prior to this commit new processes were added on threads request but the old ones were never removed
this commit adds periodical updates and now the server sends events when processes starts and terminate so debugger client UI can update

* apply PR suggestions

* rename thread maps

* update links and clarify info

* rename frames

* rename vars

* simplify frame and var handling

* Update apps/elixir_ls_debugger/lib/debugger/server.ex

Co-authored-by: Steve Cohen <scohen@scohen.org>

* PR fixes

---------

Co-authored-by: Steve Cohen <scohen@scohen.org>

Author: lukaszsamson

apps/elixir_ls_debugger/lib/debugger.ex

@@ -25,7 +25,7 @@ defmodule ElixirLS.Debugger do
     if ElixirLS.Utils.WireProtocol.io_intercepted?() do
       Output.debugger_important("ElixirLS debugger has crashed")
 
-      :init.stop(1)
+      System.stop(1)
     end
 
     :ok